2 Cold Radiators

[spongsdad]

My bungalow is heated by a Baxi Solo 3 70PF non condensing boiler. It is connected to 11 radiators and controlled by a Honeywell CM927 programmable room thermostat operating a Honeywell two port motorised valve. Hot water is supplied by means of a second motorised valve, separately controlled. This means I can run heating & hot water together or quite separately. My problem is that no matter how I set the system two radiators are failing to warm up properly. So far as I can tell, these are fed by plastic rather than copper tube. I find that the Honeywell stat gives good, close control of the system but the pump as a consequence cycles on and off constantly. The two radiators concerned are of high efficiency but low water capacity, and it occurs to me that they are simply not receiving an adequate water flow to heat them up. The system is fitted with a Fernox TF1 filter for trapping magnetite and is filled with corrosion inhibitor. I am minded to get a plumber in to repipe to these two radiators but would welcome experts' advice as to how to overcome the problem. The other radiators heat up rapidly even with the lock-shield valves almost totally closed. The pump is less than a year old.

 

[HERTS P&D]

Do these non working rads have thermostatic valves fitted to the rads?

It could be a stuck pin.

http://www.youtube.com/watch?v=nyCBMz6U6ZU

Andy

 

[spongsdad]

They do indeed. I've checked them both and they seem to be okay.

 

[HERTS P&D]

Turn off all the hot ones and see what happens.

Andy

 

[spongsdad]

Andy, I think you are trying really hard to help me. Thank you. I did that earlier today. The best I can get is tepid.

 

[HERTS P&D]

Are the lock shields open ?

Andy

 

[spongsdad]

Onthe two radiators in question they are fully open.

 

[Andy128]

Is there any difference if you run CH+HW together? Maybe having the pump turn on/ off in CH mode (coupled with a satisfied room stat), is not allowing the two rads in question an adequate chance to heat up properly.
In CH+HW mode the pump will (usually) run constantly (well, it does on my setup as we have a capillary TRV on the cylinder rather than a cylinder stat!).

Try re-balancing the system, if you can't get the flow to the rads hot enough then it's most likely a balancing issue, room stat location, or even blockage.

 

[spongsdad]

Is there any difference if you run CH+HW together? Maybe having the pump turn on/ off in CH mode (coupled with a satisfied room stat), is not allowing the two rads in question an adequate chance to heat up properly.
In CH+HW mode the pump will (usually) run constantly (well, it does on my setup as we have a capillary TRV on the cylinder rather than a cylinder stat!).

Try re-balancing the system, if you can't get the flow to the rads hot enough then it's most likely a balancing issue, room stat location, or even blockage.

Thanks Andy. Our household demand for hot water is relatively low and so the boiler does not often fire up to meet hot water demand. the radiators which are presently heating up rapidly are all doing so with the lock-shield valves only slightly open. The cold radiators have fully open lockshield valves and TRVs set at the maximum, i.e. permanently open. It is increasingly obvious that, for whatever reason, insufficient water is circulating through these rads.
My reluctant conclusion is to replace the current (plastic) tubing to them with microbore copper: not a job for me as my plumbing skills only extend to opening and closing the stopcock at the main riser. Have I exhausted all the other possibilities?

 

[Andy128]

I can't think of anything else you could do. Might be time to call an engineer in. Once they've had a look at the existing layout they'll advise accordingly.

If everything else checks out OK, they'll probably get the pipes tee'd off nearer the boiler, and maybe relocate the room stat, depends really.