2 cold rads.

[aryan57]

I have 2 cold rads on my system. I replaced 3 rads with type 22 convectors with thermostatic valves and of course, I had to drain down. My system was originally a gravity type fed by a Rayburn, then upgraded to a back boiler with a pump added. No TRV's As far as I can tell, it is a single pipe system. The 2 cold rads are fed from a single pipe. The way the system worked before was water went to a downstairs rad at the back of the living room, then to a kitchen rad, then to the hall rad then upstairs to a bathroom rad. Bathroom and hall rads heat up but kitchen rad and living room rad stay cold. I suspected an airlock and drained water from the kitchen rad. There was air in the pipes, the 2 cold rads heated up and I thought my problem was solved. But apparently, only till I switched everything off. Next day, same problem.

Assuming the problem is an airlock. I have been told that I can connect a hose to the drain cock and blast any air in the system up to the expansion tank in the loft. Is this a safe procedure?

Or has my problem been caused by me adding the TRV's? Any advice appreciated.

 

[aryan57]

Anybody? I am disappointed. I took the TRV's off, connected a hose to the drain cock and no bubbles appeared in the expansion tank. So I am left scratching around for new ideas as to why the system will not heat up. The pump runs and the only rad to produce heat is the one nearest the hot tank.

 

[lizard1975]

Ah the joys of the one pipe system
First of all connecting a hose to the drain coc k and blasting the system with water will not remove any trapped air from the radiators, only from a selective section of pipe to the expansion tank.

The two radiators that you replaced, were they of the old cast iron type or of the current ones you buy today. Also when you replaced the radiators did you move the tee joints into the supply pipe? Lastly TRV's are a serious no no with the one pipe system as they restrict the flow of water by too much. Have you bleed the two radiators that arn't working to see if any air is in them again?

PS when you say you removed the TRV's are you just talking about the plactic control knobs or the value as well? ie did you drain down the system again and swaped the TRV values for normal radiator values? If you didn't then that is the most likely cause of the problem.