DHW temperature up and down

[rob jefkins]

The temperature on a customers DHW is up and down on their vaillant combi boiler.
Is likely to be down to a faulty thermistor?

Any advice greatfully received !!!

cheers

 

[quality]

Have ya tested the thermistor for correct resistance, have ya checked the gas rate on hot water, have ya checked the manual for the spec, have ya checked ????
Not being crankey but there are many things which can cause this but heat exchanger transfer, and modulation of gas could be a start

 

[stevetheplumber]

The temperature on a customers DHW is up and down on their vaillant combi boiler.
Is likely to be down to a faulty thermistor?

Any advice greatfully received !!!

cheers

first thoughts with this problem is blocked heat exchager easy to whip it out and check for crap in it As previously said many things can cause this so go for easy checks first