Polytank feed and expansion tank (4 gallon/18 litre)

The Polytank feed and expansion tank is a feed and expansion tank produced by Polytank Group Ltd, the British manufacturer of water tanks and cisterns. As the name implies, the tank is designed to be used as a feed and expansion tank for open-vented central heating systems. It is suitable for new properties or as a replacement header tank on an existing installation. It has a capacity of 4 gallons / 18 litres.

Polytank feed and expansion tank

The tank is supplied with a snap-on lid, ensuring that dirt, insects and rodents cannot get inside, and a screened warning pipe fitting and washer, which also protects dirt and debris from entering the cistern via the overflow pipe.

You’ll also find a 15 mm Part 2 ball valve and a plastic float, and also a float valve backing plate – a small piece of plastic fitted to the ball valve shank, which protects the tank wall from the upward force of the float.

There’s also a insulation jacket for preventing heat loss, and a length of string for tying the insulation jacket around the tank. A service valve which would allow you to isolate the ball valve with a screw driver is unfortunately not included, however this can easily be purchased separately for a couple of pounds.

The tank is factory sealed, and all of the fittings are to be found inside the tank itself.

Note that while the capacity of the tank is listed as 4 gallons / 18 litres, the feed and expansion tank should never be full to this capacity when cold. The water level should be only slightly higher than the outlet at the bottom of the tank. This is so that the water in the central heating system has room to expand.


The Polytank 4 gallon/18 litre feed and expansion tank is WRAS approved, and is manufactured to BS4213:2004 and in ISO 9001:2008 approved factories.


Length: 480 mm
Width: 250 mm
Height: 320 mm
Weight: 2.2 kg

Where to buy

The Polytank 4 gallon/18 litre feed and expansion tank is available B&Q, which offers free delivery on orders over £50 and a click-and-collect service.

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Surestop stopcock

A Surestop stopcock is a stopcock produced by Surestop Ltd, a UK company which specialises in making easy to use stopcocks that are designed to prevent water damage to properties.

Unlike traditional brass-handle stopcocks which may leak or jam, Surestop stopcocks are operated via a simple rocker switch, similar to a light switch. Not only does this make them extremely easy to operate, it also ensures that the water can be turned off quicker in the event of an emergency. The control switch can be situated on the valve itself, or some distance away, making the valve even more accessible to operate.

Surestop stopcocks are also ideal for people who may find it difficult to operate a traditional brass-handled stopcock, such as the elderly or the disabled.



Surestop stopcocks are operated by the pressure of the mains water itself. When the rocker switch is pushed, the valve harnesses the pressure of the mains water to push a diaphragm against the valve seating, stopping the flow of water. This means that they do not require any batteries or their own electricity supply.

Surestop stopcocks are available in 15 and 22 mm pipe diameters, and they are also available as a “remote” version, where the switch is connected to the valve by a length of of tubing. This means that the switch can be mounted in a convenient location some distance away from the pipework, such as in the kitchen wall above the kitchen worktop, or towards the front of a cupboard near the door. The standard length of tubing is 2 metres; however it is possible to purchase tubing in 6 metre lengths, offering greater flexibility in terms of switch position. It is also possible to buy Surestop stopcocks which will connect to MDPE, the blue plastic pipework situated underground which supplies cold water to a property.

All Surestop stopcocks are WRAS approved, and can be used as a complete replacement for a traditional brass-handled stopcock, or in compliment to an existing valve. They are limescale resistant, and according to the manufacturer, can be installed by the average DIYer in as little as 45 minutes. All Surestop stopcocks are produced at the company’s factory in Birmingham, and Surestop reports that every stopcock is tested with 14 bar of pressure to verify that it works effectively.

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Why is there hot water coming from the cold taps?

Hot water coming from the cold taps – it may seem bizarre, but it can and does happen. On some occasions it is due to a hopeless plumber – this author once encountered a toilet which had been plumbed into the domestic hot water supply. Residents of the house could flush the toilet and watch the gas meter go up as the boiler heated the water to fill up the cistern again!

However, hot water coming from the cold taps is no laughing matter. Not only is it a waste of money, the consequences can be deadly. The cause is usually a failed immersion heater thermostat.


In a typical open vented hot water cylinder – that is to say, a hot water cylinder fed by a cold water storage cistern – the hot water is heated via one or two large elements known as immersion heaters. The immersion heaters may be the only means of heat, or they work in compliment to a heat exchanger inside the cylinder: a coil of pipe which carries hot water from the boiler.

Each immersion heater is equipped with a thermostat, which turns off the electricity to the immersion heater when water inside the cylinder reaches a preset temperature (usually 55 – 60 degrees Celsius). This thermostat is located underneath the metal cap which covers the top of the immersion heater, and should not be confused with the thermostat that is strapped around the outside of the cylinder.

The problem of hot water coming from cold taps or cold outlets occurs when the immersion heater fails in the ‘on’ position. This will heat the water up in the hot water cylinder indefinitely. This extremely hot water expands up the expansion pipe and vents back into the cold water storage cistern. But since the hot water cylinder is supplied with water from the cold water storage cistern, this effectively creates a loop whereby the water in the cold cistern is being heated by the immersion heater.

Since the cold water cistern usually supplies the cold taps in the bathroom, this is why a failed immersion heater thermostat will result in them delivering hot water. The kitchen tap will be unaffected as it is supplied from the mains. However, even in households where the bathroom cold taps are supplied from the mains, you may still notice this problem in the form of exceptionally hot water from the hot taps.


If left long enough, a failed immersion heater will bring the water to a boil, including the water in the cold water cistern in the loft. The danger of having up to 50 gallons of water at a rolling boil in the loft speaks for itself. While most modern plastic cisterns are able to accommodate water at such temperatures for extended periods of time, there have been incidents where improperly supported plastic cisterns have split, dumping a quarter of a ton of boiling hot water onto residents below, seriously injuring them or even killing them. In once instance, the cistern was installed on a wooden door laid across the joists.


As well as hot water coming from the cold taps, there are other warning signs which may be indicative of this problem. As mentioned by the Health and Safety Executive, keep an eye out for:

  • Excessively hot water coming out of the hot water taps;
  • Excessive noise or ‘bubbling’ from the hot water cylinder;
  • Steam/moisture in the roof space.


If the cause of this problem is indeed a faulty immersion heater thermostat, then replacing it with a new thermostat with a safety cut-out feature should solve this problem. The cold water storage cistern should be inspected for any damage, and should be checked to see that it is situated on a flat, stable, continuous base which supports the entire base of the cistern, leaving no part of it overhanging.

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How to isolate a toilet cistern – overflow or maintenance

Need to isolate a toilet cistern? Whether your loo is overflowing and the ball valve won’t shut off, or you turn to isolate the cistern for repair or maintenance, this guide has got you covered.

Turn off the isolation valve near the toilet cistern

This is the fastest way to shut off the water supply, although you will require a slotted/blade-edged screwdriver (the attachment on a pen-knife should be suitable for this).

Simply locate the isolation valve on the supply pipe to the cistern, and turn the screw a quarter turn so that the slot on the screw is no longer in line with the direction of the pipe. This should close the valve.

Tie up the ball valve

If there is no isolation valve, use some string or garden twine to tie the arm of the ball valve to a batten of wood laid across the top of the open cistern. In the event that the cistern is flushed, this will prevent the float from falling and opening the valve.

This method will obviously only work if the ball valve is working, and of course it cannot be used if the purpose of isolating a cistern is to replace the valve inside it.

If there is no isolation valve on the pipework near the cistern and the ball valve is not working or it is impractical to tie it up

Mains-fed toilet cisterns: turn off the mains stopcock, which is typically located under the kitchen sink. This will stop the supply of water to the toilet cistern immediately, notwithstanding any water that remains in the pipework. Note that this will shut off the water supply to every appliance in the household, including the kitchen tap.

Cisterns fed from the cold water storage cistern: close the gate valve on the supply pipe from the cold tank. Note that depending on the configuration of the plumbing system, this may also shut off the supply of cold water to the bathroom.

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Part 1 and Part 2 ball valves: what’s the difference?

What is the difference between a Part 1 and a Part 2 ball valve? These brass fittings are some of the most common types of ball valves found in British homes. They are typically found in loft cisterns, such as the cold water storage cistern and the feed and expansion cistern. They both work in roughly the same way: as the cistern fills and the water level rises, the float pushes the float arm up. This in turn moves a rubber washer against the valve seat, closing the valve.

However, Part 1 and Part 2 valves differ in two key ways. The first is in relation to the point on the valve where water is discharged.

On a Part 1 or ‘Portsmouth’ valve, the outlet is on the underside of the valve. On a Part 2 or ‘diaphragm’ valve, the outlet is on the top of the valve. Water is directed down into the cistern via a small plastic spout which screws onto the valve body. Should this spout become detached from the valve, then water will spray up into the lid of the cistern. This water will probably leak out from the top of the cistern. If the cistern doesn’t have a lid, it will deliver a fountain of water up into the loft space!

If a Part 1 ball valve fails and the water level in the cistern reaches the pipe centre line, there will be no air gap between the valve and the water in the cistern. This means that the outlet on the valve will be completely submerged. More to the point, it means that the valve would fail a back-siphonage test. Should there be a negative change in water pressure in the supply pipe, water in the cistern will be siphoned back into the mains. This is prohibited by water regulations and should never be allowed to occur.

As for the other reason why Part 2 ball valves are preferred? That’s because they are equipped with a specifically-designed mechanism for adjusting the water level. The position of the float on the arm can be raised or lowered via a wing nut. This feature is not found on Part 1 ball valves – the only way to adjust the water level is to manually bend the float arm.

So, the difference between a Part 1 and a Part 2 ball valve – or differences, to be more precise – are pretty straight-forward. They also explain why Part 1 ball valves are poorly suited, and why it is a good idea to replace a Part 1 valve with a Part 2 valve, especially if the opportunity presents itself.

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Tank bung

tank bung is a bung used for blocking a cistern outlet, such as the outlets on a cold water storage cistern. Typically available in 15 mm, 22 mm, and 28 mm sizes, a tank bung consists of a plug made out of rubber, or made out of plastic with rubber edges, which is inserted into a cistern outlet from within the cistern itself.

Tank bungs may also be referred to as radiator bungs – they are usually the same piece of equipment. Bunging a radiator will allow for a radiator to be changed without having to drain down the entire central heating circuit and refill it with inhibitor.

Tank bungs are used when it is necessary to shut off the supply of water from the cold cistern to another part of the plumbing system (e.g. to the hot water cylinder), and a gate valve on the supply pipe is faulty or absent.

The main advantage of using a tank bung is that a tank/cistern outlet can be isolated without having to drain down the cistern in the absence of a working gate valve, potentially wasting up to 50 gallons of potable water.

Why might I need a tank bung?

As mentioned, bunging a tank will allow you to carry out work on the plumbing system without having to pour 50 gallons of water down the drain. An example of this scenario would be if you needed to replace a washer on a hot tap, but there is no gate valve on the supply pipe to the hot water cylinder, or the gate valve is faulty.

Once a tank bung is in place, it is the ideal opportunity to install a gate valve where one is missing, or to repair one which is faulty. Valves which isolate the supply of water from a cistern are required by water bye-laws.

While it may be possible to improvise a tank bung with a cork or piece of rubber, it is possible that a device which has not been specifically made for the purpose may not cause a water-tight seal. Where maintenance is being carried out on open pipework in connection to a cistern full of water, the end result could be catastrophic if the seal should fail.

Unfortunately it is not always possible to fit tank bungs due to the shape or design of the tank connector on a cistern, e.g., the presence of brass lugs on the outlet prevent the tank bung from forming a water-tight seal. In such cases, it will be necessary to isolate and drain the cistern down.

What’s the difference between a tank bung and a radiator bung?

As mentioned, there is little to no difference – both will allow you to carry out work on a plumbing system without having to isolate and drain down the relevant cistern.

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Croydon ball valve

A Croydon ball valve is a ball valve which consists of a piston inside a brass housing, with a float arm secured to the valve via a brass split pin. On the end of the float arm is a plastic or copper float.

Inside the valve, the piston carriers a washer, which faces the valve seating. When the water level in a cistern falls, such as in a cold water storage cistern or feed and expansion cistern, the piston is moved away from the valve seating, opening the valve and allowing water to flow into the cistern. As the water level in the cistern rises, the upward force of the float pushes the piston and its washer back onto the valve seating, closing the valve.

A Croydon ball valve operate in exactly the same way as Part 1 ‘Portsmouth’ pattern ball valve, except that the piston which carries the washer moves vertically instead of horizontally.

Both Croydon ball valves and Part 1 ball valves are being phased out in favour of Part 2 ‘diaphragm’ ball valves. This is because they do not offer an effective air gap between the water outlet on the valve and the pipe centre line, increasing the risk of back-siphoning into the mains in the event that the valve should fail. Another reason why they are being phased out is because, unlike Part 2 ball valves, they are not equipped with a mechanism to adjust the water level in the cistern – the only way to do so is to physically bend the float arm.

A Croyon ball valve may also be equipped with a ‘silencer’ tube – an extension of pipe which dips down into the water in order to reduce the noise of the cistern filling. Current water byelaws prohibit the use of such fixtures on cisterns.

For the above reasons, Croydon ball valves are no longer permitted on cold water storage cisterns, and should be replaced with a Part 2 ball valve.

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Open a drain cock: guide & tips

Need to open a drain cock? Whether you’re draining a hot water cylinder or a radiator, here are a few handy tips which may make the process a little bit easier.

How to open a drain cock

Ensure the discharge point is lower than the drain-off point

Water won’t flow uphill on its own accord (unless it’s siphoned). When draining a hot water cylinder or radiator, make sure that the hose’s exit point is lower than the base of the cylinder. Ideally it should be a downstairs sink, drain or toilet. Remember that any bends or loops in the hose which are higher than the given water level in a cylinder or radiator will prevent the water below that point from draining. This could come as an unwelcome surprise when removing the hose from the drain cock.

Place an old towel or a piece of cloth underneath the drain cock

In some cases, especially on older drain cocks, water may seep out of the valve via the spindle. It is always a good idea to place an old towel or a piece of cloth underneath the drain cock to catch any drips. You can also use this piece of fabric to catch any drips when you disconnect the hose.

Use a jubilee clip to secure the hose to the drain cock

Using a jubilee clip to secure the hose to the drain cock will ensure that it doesn’t slip off or be yanked free accidentally, causing to water to leak out all over the floor.

Don’t use a pair of pliers to open the drain cock

Use a small adjustable spanner instead, or a drain cock key. Pliers are liable to damage the edges of the spindle.

Mind the hose

It sounds like an obvious one, but most accidents happen in the home. Be careful not to trip over the hose running through the house and potentially down the stairs, and don’t forget to remind others in the household of the potential trip hazard.

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Drain the hot water cylinder: how-to guide

Need to drain the hot water cylinder? Whether you need to fit a new immersion heater or replace the cylinder altogether, it’s not a difficult task.

However, unlike draining a cold water storage cistern, it cannot be done as easily as shutting off the supply and running the taps until the cistern is empty.

That’s because shutting off the supply of cold water to the hot water cylinder will stop the flow of hot water in the home, but it will still leave the cylinder full of water – even when the hot taps run dry.

This is because of how a gravity-fed system works. It is gravity acting on the water in the cold water storage cistern which effectively pushes hot water out of the top of the cylinder and off to the taps. Isolating the hot water cylinder from its supply prevents this from happening, but that’s all.

This arrangement is actually a safety precaution: it means that even if the supply to the cold water storage cistern is interrupted and the cistern runs dry, the cylinder will still be full of water and the immersion heater does not attempt to heat an empty cylinder, which could be dangerous.

How to drain the hot water cylinder

  1. Turn off the immersion heater and the boiler.
  2. Isolate the cylinder from its supply. In order to do this, close the gate valve on the cold feed pipe by turning it clockwise.
    • If there is no gate valve on the supply pipe: the cold water storage cistern must be emptied, or a bung must be fitted. Isolate the cistern via the isolation valve adjacent to the ball valve or by shutting off the mains, and drain the cistern down. Alternatively, tie up the ball valve to a batten of wood placed across the cistern. Another option is to bung the supply pipe from inside the cistern with a tank bung.
  3. Run the kitchen hot tap until it stops. This will drain all of the water out of the pipework above the cylinder, such as water in the expansion pipe.
  4. Locate the draincock at the bottom of the cylinder. The draincock is likely to be on the elbow of the cold feed, or on the cylinder itself from a small spur of pipe.
  5. Place an old towel underneath the draincock. This will catch any drips of water weeping from the spindle.
  6. Attach a hose to the draincock using a jubilee clip, and run the hose to an exit point such as a sink or drain that is lower than the base of the cylinder.
  7. Open the draincock using a draincock key or a pair of small adjustable grips. You should hear water start to flow.

Note that while this process will empty a direct cylinder (where the water is heated on an Economy 7 tariff), the heat exchanger or coil in an indirect cylinder will still contain water from the central heating circuit. In order to drain the coil, you will need to isolate the feed and expansion cistern, switch off the boiler, and drain the system down.

Don’t forget that an empty hot water cylinder is a great opportunity to remove any limescale which will have collected inside, especially if you happen to be replacing a the lower entry immersion heater.

Refilling the hot water cylinder

Refilling the cylinder is simply a case of reversing the above instructions:

  1. Close the draincock and remove the attached hosepipe. Use a towel or cloth to catch any drips from the draincock.
  2. Close any hot taps you used to drain the pipework.
  3. Open the gate valve on the supply pipe. If there was no gate valve, remove the tank bung from within the cold water storage cistern, or re-establish the supply to the ball valve so that the cistern can refill.
  4. Refill the central heating circuit (for indirect cylinders).
  5. Turn on the immersion heater and the boiler.
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Part 3 ball valve

Check Part 3 ball valve prices at B&Q

A Part 3 ball valve or diaphragm ball valve is a ball valve made to British Standard specification 1212, Part 3. It consists of a plunger and a diaphragm washer which are both situated inside a plastic housing. The plunger is partly visible and protrudes from the face of the valve. Water enters the cistern via small plastic spout on the top of the valve which directs the water down into the cistern. The float arm is secured to the valve via a plastic fitting. On the end of the arm is a plastic float which rises and falls with the water level.

When the water level in the cistern rises, the float arm pushes the plunger into the valve. The plunger in turn pushes the diaphragm washer onto the valve seating, closing the valve.



Part 3 ball valves look similar to Part 2 ball valves and operate exactly the same way – the only difference is that they are made out of plastic instead of brass. Whereas Part 2 ball valves are primarily intended for loft cisterns such as the cold water storage cistern and the feed and expansion cistern, Part 3 ball valves are typically fitted in toilet cisterns.

Interchangeable valve seatings are available for Part 3 ball valves, which means the valve can be supplied by the mains or by the cold water storage cistern. Depending on the valve and the manufacturer, you may find two different valve seatings in the box: a red one if the valve is to be supplied from a cold water storage cistern, and a white one if the valve is to be supplied directly from the mains. On some Part 3 ball valves, the valve seating which isn’t fitted can be clipped onto the arm for storage. On the end of the float arm, some Part 3 ball valves also have two screw fittings for the float, which come off from the arm at different angles. This is so that, in a toilet cistern, the float can be screwed on at an angle which allows it to float in the right position between the siphon and the cistern wall.


Like Part 2 ball valves, Part 3 ball valves have a key advantage over Part 1 ball valves, or Portsmouth valves as they are also known. The position of the outlet spout at the very top of the valve means that it is impossible for water to be siphoned back into the supply, should the water level in the cistern reach as high as the centreline of the valve.

Another key reason why Part 3 ball valves are preferable to Part 1 ball valves is because they are equipped with a specially designed mechanism for adjusting the cistern water level. This is typically a plastic nut on the arm of the valve which comes into contact with the plunger.

In addition to side entry configuration, Part 3 ball valves are readily available in bottom entry form due to their common use as a valve for toilet cisterns.


A faulty ball valve is the most common cause of cistern overflow. The float can become perforated and sink, or the arm can become jammed down by limescale or debris. The arm can also become jammed up, preventing the cistern from refilling.

The most common reason for a Part 3 ball valve to fail is wear and tear on the washer and/or on the valve seating, preventing the valve from shutting off.


Repairing a Part 3 ball valve is relatively straightforward, and can be achieved without undoing the tap connector attached to the valve stem and removing the entire assembly from the cistern. While holding the valve body with a pair of grips, use an adjustable spanner to loosen the nut against the cistern wall. Undo the nut while holding the valve body in place with your hand, and the valve can be removed. Take care not to drop the washer into the cistern as you remove the valve.

Once you have you removed the valve, you can disassemble it, and fit a new washer or valve seating as necessary.

While it is possible to repair a faulty ball valve with a new diaphragm or a new valve seating from a ball valve repair kit, replacing a faulty valve with a new one may be more convenient.

Where to buy

Part 3 ball valves are available from B&Q and Wickes.



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