Ravenheat combi LS100T fluctuating domestic hot water

[hawkpig]

Hi

My combi boiler (3 years old) has started doing an odd thing recently. It fires up normally when running hot water and heats the water to really hot.

But, if I then turn on a cold tap, the hot water temp drops significantly. (All this time the gas boiler is still actually heating the water in it). The temp then starts to come back up again and stays hot thereafter.

This is not such a problem unless you are showering and then it does this all the time.

I do have a thermostatic shower unit and have had it for 2 years with non of this bizarre behaviour happening before on this boiler.

The troubleshooter in the manual reckons I should replace the potentiometer but I don't think it is that as I can hear the switch activate when I manually alter the setting which means it is responding to settings.

I've tried increasing and decreasing the mains pressure in the house also but with little success.

Any ideas or opinions welcome? Could it be the thermostatic switch or could it be a problem in the heat echangers valve?

(The central heating works fine.)

 

[Agile]

I dont think that you have fully understood the dynamic aspects of the hot and cold water flows.

Did you really adjust the water pressure OR as I expect did you turn the stopcock to close it a bit? That has the effect of keeping the hot and cold supplies in step.

Turn off the cold input to your boiler and all flow from the hot taps should stop regardless of what you do with any cold taps. Can you try that and see what happens?

Tony

 

[ChrisR]

You may have cold water crossing into the hot at a mixer tap.

 

[hawkpig]

Hi

Replaced the diaphragm in the 3 way valve. £20 job. All sorted. Thats something they don't mention in the troubleshooting manual.

Hope this helps someone else fix their boiler