Unless hot water on, overheat stat. blows

Worcester Combi boiler

Installed 2 new radiators 6 weeks ago, no problems. CH installed originally (by me) 4 years ago and has worked well.

Have been working abroad for the last month, while abroad, the boiler started playing up.

1. The auto air vent failed, needed replacing
2. The pressure safety relief valve failed (CH), replaced

Now the CH only runs if the hot tap left running, if not the boiler becomes very noisy and after approx 1 minute the overheat stat blows.

Only just got back and not worked out whats going on, need inspiration.

O/heat stat trips because heat is not being taken away. Probably the pump is siezed, or diverter valve stuck. Is it gas or oil? which model?

Woosta 35 and 350 have a pump for each - maybe its the CH one?

Thanks for the feedback.

No H/W unless C/H on., obviously problem with flow switch / circuit board (related or additional problem I don't know as yet)

Only 1 pump, no diverter valve listed in parts list/ cant see /locate one.

Problem solved

Original problem caused the boiler to overheat, which damaged fibre washers on H/W flow switch causing a leak.

Helpful neighbour? had replaced same but inadvertently replaced flow switch in wrong direction. Now rectifed, H/W fine, problem remains on C/H side.

Gas pressure not modulating, remains full on.