Worcester 28cdi - heating demand ON - flame keeps turning of

[Trowj]

Hi
I have a 28CDI
DHW works fine
CH demand comes on and boulder will work for a few min
The the flame is shut off - CH light remains on, pump still running.
After a while fires up again for a couple of min - repeat... Repeat ..
Only heating the nearest rads.
Flow out of boulder hot
Return Luke warm - so it's not up to temp.

Any ideas ?.
Vent problem ? - fan seems to be running
Overheat ? - how do I tell ?
No flashing lights - so difficult to diagnose..

Ant help / advise would be great - don't want to get ripped off

 

[Terry lambert]

It soundsclike you have a circulation problem. The boiler is shutting down because it cannot get the heat away the boiler.

So I would check all rad valves are open, if TRVs take the heads off and make sure the pins are not stuck down.

Could be blockage or weak pump

 

[Trowj]

Thanks for the reply..
Makes sense..
The pump feels very hot..
The towel rails in the bathroom /shower room ( direct off the flow & return ) nearest the boiler get red hot.
All others ( that are fed from a 10mm manifold ) just get Luke warm.
Blockage in manifold ?
I just did a system flush about 12 months ago and it was not that dirty.
Weak pump - can I test it ?
Air lock ?
..
Any more thoughts appreciated...

 

[Trowj]

Stop press..
Isolated half the rads nearest the boiler..
The rest started to warm up..
Looks like a flow problem.. - I guess pump has got a bit lazy..
Thought ?.
£157 from plumb centre - err no
Any cheaper sites ?

 

[Terry lambert]

Look at Abcot

 

[Terry lambert]

Could still be a restriction/ blockage somewhere. Rather than a lazy pump

 

[GavThePlumber]

Are rads balanced?

 

[Trowj]

It's not the pump..
Changed that with no change
Flushed system - no blockages
Now the nearest Rad won't even get warm despite the pump running for ages
Flow & Return do get warm - but I think this in conduction from the boiler..

Could the diverted valve be stuck ?

DHW is fine (very hot at first demand )

Thoughts ... ?

 

[Rob]

Check the return inside the boiler. It should be the same temp as the return underneath the boiler.

Diverter may be seized as you say which would also explain why the HW is very hot to start with.

 

[Trowj]

Thanks for the reply..
Colder below ..
Is there anyway of moving the valve manually ?
Is it a common spindle that activates the DHW switch ?

 

[shopwherever]

It seems that I have the same problem, can you tell me how did you resolve it?
Thanks

 

[Trowj]

Will do..
Unless you get there first !
I am going to strip the diverter valve tomorrow..
Will update with results..

 

[shopwherever]

Will do..
Unless you get there first !
I am going to strip the diverter valve tomorrow..
Will update with results..

Try to turn the room thermostat and HW off and see if the pump and boiler continue indefinitely. That will mean that the valve is locked and is requesting the boiler to heat the HW cylinder. If the do stop, then it may not be the motorised valve.

 

[Trowj]

First shopw
The 28cdi is a combi and does not have a tank or motorised valve but thanks for the reply.
..
Fitted a new diverter valve ( £78 in Vat )
Everything now back to normal..
..
When I look back it was staring me in the face ..
When the heating kicked in - the sticky ( then stuck ) diverter valve would only allow a limited amount of HW into the Heating circuit. Then none.
Most was passing thru the DHW heat exchanger (very hot ) and the bypass.
So the boiler would cut the flame on overheat..
Turn the DHW on and you got a plug of Very hot water ...
..
( I emailed Worcester support and they did not point the finger at the D valve !! )
..
Fitter a new diverter rather than try and clean it out.. Then new one looks better construction inside.
..
Going to give the system a good flush once the weather gets a bit nicer !
..
Thanks for all the advice given - much appreciated..