Vaillant Ecotec - Hot/Cold/Hot water

[JayUK]

Hi all,

I have an old Ecotec 837 combi and experiencing the usual hot/cold/hot cycling issue with my DHW.

If the flow is around 5L/min it goes hot/cold/hot/etc. If I increase the flow slightly it stays hot.

I cleaned the plate heat exchanger with brick acid, but it was still slightly blocked (I could hear trapped water inside sloshing about). I then managed to get hold of a used plate heat exchanger. I also cleaned that with brick acid (I think it had a slight blockage too), but still experiencing the same hot/cold cycling issue (I don't think that was fully unblocked).

The CH pipe from the diverter is getting warm with the DHW on. The diverter was replaced a few years ago.

The temp sensors seem to be reporting the correct temps and are changing according to as the pipes heat up/cool down.

The cartridge filter has also been replaced. The pump seems to be running ok.

Before I spend on a brand new plate heat exchanger (not a reconditioned one), does anyone have any suggestions/advice as to what else it could be?

Thanks,
J.

[gas4you]

you seem to have covered most things, but if the boiler is cycling and not shutting down it still points to the plate being blocked on the system side.

Have you cleaned/replaced the canoe filter?