no heating downstairs

[rawahk]

sorry for a dumb question beforehand

we are having a strange issue where our downstair heating is not working on a S plan open vented system. the upstairs ones works fine. things tried so far

1. radiators professionally flushed
2. changed water pump
3. regularly bled radiator but they dont bleed any air
4. bled pump and automatic air vent

Both old and new water pumps get really hot and so that flow and return pipes on the boiler. The boiler kickstarts but trips when the cut point is reached.

The strange bit is that randomly the heating does come on (both upstairs and downstairs) if we let new water pump work for a bit and then swap it with old one but only till the heating is switched off next time and then again nothing afterwards.

Any suggestion would be greatly appreciated

 

[Deleted member 120897]

Sounds like it could be a motorised valve failure

 

[rawahk]

Sounds like it could be a motorised valve failure

we have 2 separate valves and they both open and close fine i have tried running just the CH and that does not help