Ravenheat 820 20

Hi all, has anyone come across a fault on a ravenheat rsf 820 20. Heating is ok, but when hw is called for, the burner ignites, but no hw comes from the boiler. After the heating is on for around 5 mins, hw is available but at a low pressure. I am thinking hw sensor or div value, but the hw at low pressure is throwing me. Any help is most welcome thanks

Hi normally the fault would be down to the diverter valve because the power from the boiler pushes down the heating pipes the diverter valve should close off the port to the heating when calling for water only
If you have low water pressure coming out it could be the mesh filter thats fitted on the hot water outlet from the diverter valve,
There is not a plate heat exchanger on these boilers they use a type of bithermic heat echanger that can get corroded inside causing water to pass through slower,
Also these boilers do not have sensors as others do, they have stats with a phial tube attached to the relevent pipes to register the temp.
I would say try replacing the diverter valve
Another thing you can try is turn off the heating service valves but beware they will leak when you turn the screws to the off position
they mostly do stop leaking after they are put back to the same position and some heat is put on the pipes
The diverter valves are not cheap ? well original ones ? but as its an old boiler after market replacements are now available but again beware some have not got the same springs inside and you may find things like your washing machine does not work properly and can close the boiler down sooner than it should


best of luck let me know Mick