I know this is an old boiler. But I'm hoping that the issue I am experiencing can be resolved without resorting to replacement of boiler.
CH works fine. The problem is with DHW. Open HW tap and boiler fires up. Water at tap gets hot. Temp gauge rises to about 70C and burner goes out (as expected) but the temp drops to 50C before boiler fires up again by which time water at tap has gone cold. Then the temp rises back up to 70C before burner goes out and so on.
Had CH system power flushed. Replaced DHW thermostat which is set to max. Divertor valve is working fine (pin lifts and operates micro switches, no leakage to CH circuit). Descaled secondary heat exchanger (by pumping Furnox DS3 round DHW circuit).
So the 20 degree spread from 50C to 70C seems rather high which looks like the cause of the wild temp fluctuation at the HW tap.
Does anyone know whether this is normal or what likely cause is and fix please?
CH works fine. The problem is with DHW. Open HW tap and boiler fires up. Water at tap gets hot. Temp gauge rises to about 70C and burner goes out (as expected) but the temp drops to 50C before boiler fires up again by which time water at tap has gone cold. Then the temp rises back up to 70C before burner goes out and so on.
Had CH system power flushed. Replaced DHW thermostat which is set to max. Divertor valve is working fine (pin lifts and operates micro switches, no leakage to CH circuit). Descaled secondary heat exchanger (by pumping Furnox DS3 round DHW circuit).
So the 20 degree spread from 50C to 70C seems rather high which looks like the cause of the wild temp fluctuation at the HW tap.
Does anyone know whether this is normal or what likely cause is and fix please?