Two CH loops - one working, one not

[Matt21]

I have a Keston 80 running two CH loops (rads on primary, underfloor on secondary) via two Grundfos pumps and two Honeywell zone valves. The primary pump is in sequence with the secondary one, and they are separated by the secondary zone valve so that unless the secondary zone valve is opened, the secondary pump stays switched off and the underfloor heating does not come on.

If I try to operate the underfloor loop, the zone valves appear to be functioning properly (secondary opens, primary closes), but though the boiler fires, the heatng doesnot come on. The pipework immediately after the secondary zone valve remains cold at the junction where the return pipe joins it - almost as though the pump is drawing cold water from the return pipe and not the hot water coming from the boiler. The boiler then intermittently cuts out and the pipework around feels extremely hot.

Any ideas? cheers

 

[waterworks]

Sounds like air in system.

 

[Matt21]

Yes, that crossed my mind. I have bled the pumps, but what else can I bleed on an underfloor system?? How do i get rid of the airlock?

Cheers

 

[waterworks]

You could try shutting valves on your other circuit, so that water is forced to go through your underfloor heating.

 

[Matt21]

Hmm - cunning plan - will go have a bash!

 

[Matt21]

No joy. I can hear air bubble type noises running through the pump, but can't get rid of it. Not even sure if this is the problem tbh. Is there an easy way to get all the air out of the system?