Radiators luke warm

[bluebouye]

Please help! I installed 7 new rads (and new TRV's) mostly doubles to my 3 bed semi a year ago, (I have a one pipe CH system), i then replaced the boiler with a Heatline condensing in the summer, it was all tested and the rads were piping hot. Then, when the weather started getting cooler started using CH, but all the rads upstairs were hot but the two downstairs are warm but not hot. The pipework and valves coming out of the floor feeding the two rads downstairs are so hot you cant touch them but the rads are just not getting hot enough and the water is obviously not flowing through them. I have drained the system (clean as a whistle), checked the valves to see if there are any blockages (none), all the rads are bled. My plumber came round scratched his head and said he didnt know why it was happening and i should consider putting the two rads downstairs on a seperate loop connected to the boiler! Should i do this? What i cant understand is why it all worked perfectly before and not now. Any help appreciated.

[Mike Jackson]

What speed is the pump set on? With a one pipe system the heat is transferred into the radiators from the pipework underneath by gravity convection. If the pump is set too fast the rads don't always heat up.

Mike

[bluebouye]

Cheers Mike. I was told there was no way of adjusting the speed on the pump is this true of pumps on new boilers?, my plumber did mention something about installing a valve to reduce the flow rate. I am not a plumber but have a basic understanding of ch systems.

Dean

[Mike Jackson]

Originally Posted by bluebouye

Cheers Mike. I was told there was no way of adjusting the speed on the pump is this true of pumps on new boilers?, my plumber did mention something about installing a valve to reduce the flow rate. I am not a plumber but have a basic understanding of ch systems.

Dean

Depending on the circuits it may be possible to install some sort of balancing valve to promote flow through the cooler radiators but a better solution would be to convert to two pipe. Didn't realise the pump was integral to the boiler, you shouldn't turn these down.

Mike

[Tosh]

Have you balanced the system correctly? It can take a bit of fiddling about to get the balance on all the rads correct.
I had two rads on my system that were luke warm while the rest were boiling until I balanced the entire system correctly.
With the cooler radiators you could always bleed one of them or all of them to draw the hot water through from the hotter rads and then top up the water pressure at your filling loop.