Hot water is too hot! Combi boiler or hot water cylinder

It’s not only annoying if your hot water is too hot all of a sudden, it can also be dangerous. In this article, we’ll take a look at the most common causes for this problem and some of the solutions to it.

Hot water is too hot

There are several reasons why it’s a really good idea to fix this problem as soon as you can. The obvious one is that sudden, unexpected changes in water temperature can cause scald burns. This is especially true for:

  • Young children – their skin is much more susceptible to burns than adults.
  • Elderly and the disabled – they may not react fast enough to prevent injury, or may injure themselves while trying to avoid contact with the hot water.

Other really good reasons to fix this problem:

  • It could be a symptom of a more serious plumbing issue.
  • If your water is hotter than you actually need it, it’s a waste of money.

I have a combi boiler

If you have a combi boiler, the first thing to check is the settings on the boiler itself. Has the water temperature accidentally been set too high? The ideal temperature is 50 to 60 degrees Celsius.

If the setting is OK but the water is still too hot, there could be a problem with the boiler’s internal components. This kind of job should only be done by a qualified heating engineer, as it is illegal for individuals who are not on the UK Gas Safe register to work on a gas appliance.

I have a hot water cylinder

If you have a hot water cylinder, the first thing to check is the thermostat strapped around the cylinder. The best temperature is 55-60 degrees Celsius. Anything lower than this can encourage the growth of Legionnaire’s disease in the cylinder. Anything higher, like 70-80, will almost certainly be too hot.

If the temperature is at the correct setting, is the thermostat properly secured to the cylinder. Is it in contact with its copper surface? If it isn’t, the boiler won’t have an accurate idea of the water temperature inside the cylinder and may overheat it.

The same is true if there is condensation on the cylinder. The condensation is the result of high humidity in the room.

Cylinder thermostats run on mains electricity. Always isolate their power supply before working on them. Never attempt to work on them yourself if you cannot competently and safely work with electrical components. If you in any doubt, call a qualified tradesman.

Immersion heater thermostat

Your cylinder may not have a thermostat, but its immersion heaters do. Once again, the best temperature for these is 55-60 degrees.

In order to check this, it’s necessary to remove the cap off the immersion heater, which will expose the electrical fittings. Like cylinder thermostats, immersion heaters also run on mains voltage power, and you should never attempt this yourself if you cannot competently and safely work with electricity. Contact a profession – it’s not worth the risk.

Broken thermostat

While most modern thermostats simply won’t work if they fail, some older ones will fail in the “on” position. This is a seriously dangerous fault which can bring the water in both hot and cold water tanks to the boil. There have been incidents where the cold water tank splits, sending a cascade of boiling hot water onto the residents below.

Symptoms of this fault include:

  • Extremely scalding hot water from bathroom taps.
  • Hot water coming from cold bathroom taps.
  • Rumbling, gurgling sounds from the hot cylinder.
  • Moisture/steam in the loft space.

Click here for our article on this problem.

Faulty motorised valve

Another possible cause for this issue is a problem with your motorised valve. This valve controls whether water from the boiler heats the radiators or the water in the hot cylinder.

If the valve has failed, the thermostat in your living will activate the boiler, but instead of heating the radiators, the water will heat the cylinder. A classic sign of this is hot water that’s too hot, and radiators that aren’t warming up properly.

 

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