System Boiler problem Aaaaarrrrhhhh!!!

1norab

Hi, I have an Ideal mini S28 System boiler. the problem I'm having is the CH works fine but if i press for DHW, the boiler cuts out. If I call for DHW only, the boiler fan/pump starts and the motorised valve starts. But just as you think the boiler is going to fire up - Nothing. When I put the boiler into system mode the lamps (x3) tell me its a Faulty Primary Circuit fault (No water or absence of flow).
Now, I'm no expert (If I was, I wouldn't be typing this I suppose), but please correct me if I'm wrong, the thermistor and the Primary circuit flow switch cannot be at fault if the CH is working. I was going to change them but then this occured to me, so I didn't. It could be the PCB but in case it 's not, what else could it be?
Any suggestions would be appreciated greatly.

Browntoa

there is normally a valve that senses the demand for hot water and should switch the water flow from the heating part to the DHW part (converta valve) . It uses a small diaphragm to operate , but it's not unknown for these to get small pinholes in , or the valve itself to stick

this is the part

http://www.boilersparesdirect.co.uk/parts-online/shopexd.asp?id=30316

1norab

Hi browntoa, Thanks for the quick response, but I dont quite understand this. According to what I see on the schematics pages of the manual, only Ideal combi C24,C28 and C32 have diverters. Where as, my S28 doesn't require a diverter as its a System boiler with a motorised valve on the flow from the boiler to the CH and another motorised valve to the DHW.
Although, that said, you could be right as why else would it be on the spare parts site???
Could this be known as the Main switch membrane. On the Ideal web page, http://www.idealboilers.com/docs/pdf/mini_manual.pdf on pages 11 and 54/55 it shows the diaphram behind the Primary circuit flow switch. Could I not just clean it to unstick it. Or was you talking about the gate valve behind the motorised valve being stuck.

Browntoa

wonder if its part 27 ?? which will divert water into part 29

1norab

Parts 27 and 29 are not present in my "S28" boiler. Only in the "C" range.

Browntoa

canucklehead is the heating expert , hopefully he will read this thread later and advise

1norab

Thanks for your input. I really appreciate any help. I am losing the will to live as this is driving me potty...