Heating issue, just got worse

[WanderOverYonder]

I posted the other day that one of our radiators had stopped heating up (it was a split of two rads from one old one) and got some advice.
I tried the bucket test that was suggested and hot water came through.
However, this evening all of the radiators (all 9) have now stopped heating up.
The boiler fires up and the boiler flow out gets burning hot but the return stays cold. The boiler shuts off and the pump (which has gotten incredibly noisy) moves the water. Each of the radiator flow pipes heat up but the stay cold and the rads only get lukewarm. The heat then dissipates and the boiler fires up again. This cycles every 30-40 seconds.

Had a look at where the pump is and the unit is hot and I mean HOT. The flow pipe away is hot but the return is cold.

I have tried drawing water through it using the drain cock and also put a hose on to one of the rads with a drain but hot comes through and then just cools.

What could be causing this, and what could remedy it? Obviously not an ideal time of year for this to happen with temps in the minus figures.
Cheers all.

Edit to add: noticed that there is a motorised valve on the return pipe to the boiler. Is this normal?

 

[Jay32Heating]

What boiler is it?

 

[WanderOverYonder]

Worcester Greenstar Ri

 

[Jay32Heating]

Hmm... I've just noticed you have said there is a motorised valve on the return pipe at the boiler?

 

[WanderOverYonder]

Hmm... I've just noticed you have said there is a motorised valve on the return pipe at the boiler?

Well, it's in a crawlspace behind the HW cylinder. You can see the two pipes come through the floor from the boiler (which is downstairs in the WC) and one goes to the pump and then branches off to the HWC and off through in to the bathroom and the first rad. The other pipe comes back in from the bathroom, to a motorised valve and then back through the floor to the boiler. This one is cold while the one feeding the pump is burning hot.

 

[Jay32Heating]

Well, it's in a crawlspace behind the HW cylinder. You can see the two pipes come through the floor from the boiler (which is downstairs in the WC) and one goes to the pump and then branches off to the HWC and off through in to the bathroom and the first rad. The other pipe comes back in from the bathroom, to a motorised valve and then back through the floor to the boiler. This one is cold while the one feeding the pump is burning hot.

OK so is you're hot water cylinder hot and hot water is working?

 

[WanderOverYonder]

OK so is you're hot water cylinder hot and hot water is working?

Yes, HW seems to be fine. The feed to the HWC is very hot.

I should add there is another motorised valve after the pump and after the branch off to the rads but before the HWC

 

[DP]

Try manual position on the ch valve

 

[WanderOverYonder]

Try manual position on the ch valve

Would that help? The return pipe is cold either side of the valve.

 

[Jay32Heating]

And the flow pipes to all the rads are hot but rads are cold?

 

[WanderOverYonder]

And the flow pipes to all the rads are hot but rads are cold?

Yes, when the boiler cuts off and the pump runs, the flow pipes at the TRVs are all hot. Some of the rads upstairs get warm but not hot, the returns stay cold and then the rads cool down as the flow pipes cool.

 

[DP]

Would that help? The return pipe is cold either side of the valve.

That would suggest the ch valve is not opening.
HW valve opens hence flow pipe red hot

Would think the motorised valve auxiliary switch not wired to run the boiler

 

[WanderOverYonder]

That would suggest the ch valve is not opening.
HW valve opens hence flow pipe red hot

Would think the motorised valve auxiliary switch not wired to run the boiler

Would that likely have just happened as it has been working fine up until this evening.

Edit to add, the motorised valve is definitely closed as the lever moves about 10mm then has resistance. Should I move it to the manual open position? Will I need to do anything else or should that start the return flowing?

 

[DP]

Motor can fail anytime.
Correct procedure of operation is......timer activates, it's zoned thermostat, if calling for heat, powers motorised valve. When valve opens, end of travel switch operates boiler

Sometimes the thermostat opens the valve and fires the boiler, so, if motor in valve duff, valve stays closed but boiler fires.

 

[Jay32Heating]

From the description it sounds like you have separate zone valves for your heating and hot water systems. if your hot water is working fine then the pump is excluded from the issue. there may be an issue with the heating zone valve. it is a strange situation you've got though if the flow pipes to the rads are getting hot still. I take it you're not using you're immersion heating back up on the cylinder too?