I have been having a problem with my Vaillant WCW – sine 18 T3WFH boiler recently. The hot water output seems to be surging and recently it’s been getting worse… almost to a rhythm sometimes. The water temperature seems to be fluctuating now too.
I recently hooked up a new washing machine to the hot water outlet (old one was on the cold outlet only) and a few months ago (just before the problems) the water mains were shut of for local maintenance while the boiler was still on so I’m guessing the pump damaged and/or on it’s way out.
Is there something I can do to check what the issue is? What would a new pump cost in the UK?