Hi,

I have a Vaillant 824E. When I turn on the hot water is comes hot for a few seconds then goes, luke warn then cold. I though it would be the temprature sensor which I just changed but no joy. When I turn the water on the burner keeps going on and off which is causing the water to go hot & cold. Anybody have any ideas.

Thanks Prav

Prav, December 2008

You're not alone. I have an 8 year old 824E that does the same thing - and it probably is the heat exchanger. How strong is your hot water pressure? Mine is very poor. Quite expensive replacement job; you may as well replace the boiler.

Simon, December 2008

DHW heat exchanger\plate heat exchanger is blocked scaled up.
either de scale it or replace it

justeve, December 2008