Beerlover, you were spot on! I took the pipe off below the rubber section and lo and behold the brass T union was fully blocked with metal flakes- no filter as such, but the bore reduces dramatically inside the T which was where everything was getting trapped. Cleaned out and hey presto, working...
Thanks Beerlover, I'll check for the filter later. Other than just replacing the part, is there any way of checking the flow rate through the heat exchanger to prove it's blocked?
Any ideas?
I've got a Vaillant Ecomax 824, approx 8 years old, which was in the house when we moved in.
The hot water temp started fluctuating hot/cold every 30 seconds or so. Online forums pointed towards the secondary heat exchanger being blocked- so I ordered a new one and in the...