Before having to dig up the lounge to find a leak, we called a plumber in who says we have no water leak. Ideal have been out 4 times in the last 2 months who say that because the pipe at the back of the boiler is red hot, the problem is definitely a leak on the hot water. No probs whatsoever with hot water but heating fires, comes on for a little while and then goes off. C
an you please shed any light? Ps: The engineers do not even look at anything once they realise the pipe is hot.
If your Isar shows a 'd' or 't' for most of the time then the boiler thinks it has a demand for hot water. The reason for this is that Isars dont look for a flow of water to switch the boiler on for hot water it looks for a drop in temperature.
You are probably aware that you have a pre heat facility on the boiler that fires the boiler up from time to time. The boiler will pre heat when the DOMESTIC HOT WATER THERMISTER senses a temperature that drops below 30 degrees C.
If the domestic hot water thermister constatnly senses a drop in temperature (which would be caused by a water leak on pipework somewhere) the boiler will stay in hot water mode, thus not allowing the Central heating to work.
The most common reasons for this are
A dripping hot water tap. Check all of your hot water taps. Any drips at all will cause this problem so if you have one get the tap fixed.
A water leak on the hot water pipe from the boiler somewhere to all or any of your hot water oulets.
A mixer thats not shutting off internally properly ie a shower or a tap.
A check that can be done would be to turn off the cold water supply to the boiler at the isolation valve. After doing this the boiler will show a 'c' in the display and the HEATING will work. The reason it will work is because you would have turned the demand for hot water off (which in this case will be one of the problems listed above).
If you can isolate appliances or showers to see if this problem stops then you can trace the cause by doing this.
The DOMESTIC HOT WATER THERMISTER being faulty shouldnt cause this problem as when it is faulty a fault code of H3 is displayed in the status window,
I hope this helps.
Please do not touch the boiler as you will need a registered gas installer to do so.
Regards.
