DIY Doctor

is it a blockage/ isn't it a blockage, that is the question.

Postby AdamsHeating » Fri Oct 10, 2008 9:58 pm


I'm stumped and it is probably quite simple! I went to a job today, Worcester Bosch Greenstar junior 24i combi.

Hot water - check
Call for heating - check ... but wait a minute... no heat from the rads...

after about 20 seconds the central heating cuts out but doesn't go to fault code. The diverter valve is fine doing its job.

I put the big kettle into service mode to fire up central heating on full blast, comes on for 20 seconds and goes off, doesn't re light, no fault code.

The pump is red hot, the flow pipe is red hot, the return pipe is ice cold, is there a blockage?

I know i'm being an amateur here. My thoughts are it is blocked somewhere on the flow pipe. Pipes start at 22mm and are on Microbore to all the rads, not all rads have TRV's and all lock shields open. I emptied out the system, filled her back up, still nothing. I haven't got power flushing equipment so i'm uncertain how to clear it now even if it is a blockage. HELP!!!

Goes to prove that even though I can fit them, doesn't mean I can always fix them!

Cheers for help,

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Simply Build It

Postby nitro23456 » Sat Oct 11, 2008 6:33 pm

gotta be a blockage or airlock really.
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Postby Steve the gas » Sat Oct 11, 2008 7:37 pm

Take the big screw out of the pump for a minute whilst its running
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Postby screech » Sat Oct 11, 2008 11:18 pm

i've had pumps pack up on these without a fault code coming up
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Postby htg engineer » Sun Oct 12, 2008 11:48 am

If all radiator valves are open, boiler flow and return isolatio valves open and you have vented the pump.

I'd be looking towards the pump being the fault, it may be a broken impeller or just a faulty motor - enough to circulate the water around the boiler for the hot water but not for the heating.

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Postby AdamsHeating » Sun Oct 12, 2008 3:55 pm

cheers for the help you lot, I'll check the pump and see if that is playing up.
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