Vented central heating system

[Jitzer]

UPDATE- just opened up all lockshield vales and trvs upstairs on 4 medium sized radiators(single convector) 3@ 2ft x 2ft and 1 @ 4ft x 2ft and all of them are red hot, however they have sucked what little heat I had from all the downstairs radiators

 

[chrishutt]

So problem is with downstairs rads or their pipework. Take one off the wall and check flow from pipes feeding it. Are these rads fed by "drops" from the floor above? What size are the pipes to these radiators?

 

[Jitzer]

yes the pipes are dropped down the walls to the radiators(concrete on ground floor) flow from pipes with rad off seems good-pipework down all walls is 15mm

 

[Jitzer]

if the pipework is clear,it seems possible that 15mm wall runs are not up to the job .-short of doing a whole re-plumb around the house ,would converting it to a sealed system by buying a sealed system kit(boiler instructions say it will work on a sealed setup) possibly improve matters

 

[chrishutt]

No, I can't see any reason why a sealed system should work any better. And 15mm is more than adequate for the pipe drops. Are you absolutely sure the pump is working properly, on the highest speed setting?

Otherwise there must be something blocking the pipes, although this might be on the pipes that supply the upstairs and downstairs rads. Is there anywhere where an airlock might have formed? Is there a filter on the CH pipework?

 

[Jitzer]

I know you said that 15mm is adequate for the pipe drops but should the pipework leading to the drops be 22mm as we notice that there is a lot of 15mm pipework under the floorboards.

We changed the pump a couple of months ago and it does appear to work harder on speed 3 although it doesn't make any difference to the amount of heat produced.

There doesn't appear to be a filter on the ch pipework. Airlock is always on my mind but we have bled the system to death, tried to force any air that may be in the system into 1 rad and bled that and always with the pump off.

 

[chrishutt]

You could have a point about the amount of 15mm in the system. Roughly speaking 15mm pipe can carry up to 7 kW, above that load you need 22mm. So you can check the radiator outputs and add them up for each section of pipework and see if it's seriously undersized.