Which is to blame? The Vaillant boiler or the timer/temp

27 Nov 2009
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United Kingdom

I have a Vaillant Ecotec Pro 28 that was installed less than 2 years ago. The electrics were also replaced at the time with a brand new electronic timer and a remote temperature controller.

The heating works fine when it is on (timer is on and temperature is also on) but when I shut off the timer or the temp. the boiler still fires regularly. The kicker is that it only fires the pump but not the gas so the radiators are cold.

So, should I call Vaillant (the boiler is under warranty) or should I call the installer?

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Are you quite sure this is not just the DHW preheat?
Are you quite sure this is not just the DHW preheat?

I am sorry but I don't know what the DHW preheat is. This did not happen last year when I turned off the heating. Basically it is as if I did not turn off the boiler but without heating up the radiators.

Edit: Just thought that you meant the hot water. If so then it isn't because the boiler fires at night when noone is using the hot water.
Try turning of the pre-heat function to rule it out completely, turn the hot water temperature selector all the way to the left to the '-' symbol and then back up to whatever temperature you require. The green light should not be on when pre-heat is off.

BTW we had a similar issue, the boiler pump and fan would come on and then quickly switch off but this was when you opened and closed a cold water tap, this was caused by a 'dead leg' of old hot water pipework.
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Hi David,

Thanks for the help. I did as you instructed and the green light turned off and did not light up again. Would this be it? I have to wait sometime to see if the boiler fires by itself even though the timer and temp are off. I will report back.

After turning it off as you indicated it has been silent. So I read your answer again and then went looking for clues in the manual and found the "warmstart" feature. It is a feature! I must have turned that on ages ago (by turning the water temp. knob all the way to the max) without knowing it...

Well at least it is not a fault but it is unexpected behaviour and possibly expensive too as it keeps the water in the boiler at a constant temperature. Doh!

Again, many thanks for your help.


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