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Central Heating

Combi boiler intermittent hot water in shower

A couple of days ago I was running a bath and the water ran cold - if I turned the tap off then on again I would get hot water for a few seconds then it would go cold. I checked the boiler (Vaillant EcoTec approx 7 years old) and discovered the pressure had fallen to 0.5 bar. I topped up the system to raise the pressure to 1.2 bar. Now we have hot water again but the temperature in the shower is constantly cycling between very hot and lukewarm, in bursts of a few seconds. Observing the boiler while the shower is running it appears to be firing for a few seconds, shutting off for a few seconds and then firing again (the flame symbol appears and disappears) in a way that appears to coincide with the temperature fluctuations in the shower. I tried topping up the pressure a bit more (to 1.5 bar) but this has not resolved the problem. Am I right in thinking that the boiler should be firing continuously while hot water is being drawn? Any ideas what the problem might be?

2 Answers from MyBuilder Heating Engineers

Best Answer

YES YOU ARE CORRECT THE BOILER SHOULD FIRE CONSTANTLY WHEN DRAWING OFF HOT WATER .I WOULD SUGGEST THAT THE DOMESTIC HEAT EXCHANGER COULD BE BLOCKED AND WATER IS AT SOME POINT GET TO HOT THEN THE BOILER THEN SHUTS DOWN AND REPEATS IT SELF MOST EXHANGERS CAN BE REMOVED AND CLEANED BUT WOULD ADVISE TO GET VALAINT ENGINEERS INVOLVED AND WOULD REPAIR AND SERVICE FOR A SET FEE.

2015-07-22T14:45:02+01:00

Answered 22nd Jul 2015

Better to fit a new plate heat exchanger rather than clean it, as the water ways are very narrow and not always can be thoroughly cleaned!

2015-07-26T21:35:02+01:00

Answered 26th Jul 2015

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