On Monday, 26 March 2018 21:39:44 UTC+1, Harry Bloomfield wrote:
tabbypurr brought next idea :

My Vaillant does that.

Is that a conventional / open vented boiler, if so you need to let
Vaillant know that they do actually produce one.

I am aware that it is often fitted to sytem and combi boilers.

condensing non-combi, 400 series IIRC. IIRC it's an installed option not always present.


NT