I've made my heating system worse!

[Rob Foster]

The reason they are not currently working is probably an airlock, even with all other rads closed this can still happen. The reason they originallt wasnt working as well as the rest of the house is likely undersized pipework. You can feed 2 rads off a 15mm supply but it depends where those 15mm pipes are tapped off the existing system. If they come off other 15mm feeds then they will suffer with poor flow.

I once tried 2x big rads doubles rated at 6kw total on a 15mm feed and rtn ....no chance it was in my gaff so didnt matter just banged some 22mm in and lovely Rob Foster aka centralheatking

 

[doitmyself]

600 x 1400 & 600 x 700 (mm) both single skin (is that the right word?). They worked ok before but not as hot as the main house

That's 1400W and 700W (Stelrad Elite K1), which are both well within the capacity of 10mm pipe. The total, 2100W, is also within the limits for 15mm pipe.

The fact that they are 'not as hot as the main house' suggests that the system has not been properly balanced.

 

[Rob Foster]

To remove persistant airlocks, connect the lowest drain off via a hosepipe to the outside tap, use jubilee clips, test water tightness open drain off and let mains pressure into the system gently. go round rads lowest to highest bleed. watch out if the F &E tank overflows . blip pump on and off . switch off mains water. run heating see if this works then disconnect the temp connection. pat self on back, let us know hiw you get on. Rob Foster aka centralheatking

 

[dan_the_plumber]

Could be a balancing issue. Turn off all rads apart from two problem rads. Do they get hot? If they do we know they are piped correctly.
Then turn all rads on. Find the ones which are piping hot and turn lock shield valves down, this will hopefully save hot water and leave enough in reserve for the two other rads.
If your problem is caused by an air lock, you may be able to feel heat above head height on the drop downs. The pipes will be hot up high but cold down low.
Ok so now hopefully you’ve got a drain off on or near radiator. Attach a hose pipe, get someone else to open filling loop, to blast air out through hose. Close everything off again and retry.

 

[Ivan Android]

Thanks to everybody who offered advice, it's all been very helpful.
I've got about as much heat back in the problem rads as there was before I started changing valves by using a combination of the suggested techniques.
I think the problem mainly lies with undersized pipework so will take a stab at replacing the 10mm with 15mm in the warmer months.
Does anybody see any benefit to using something bigger than 15mm when that's what I'm going to be connecting it to?

 

[Rob Foster]

Thanks to everybody who offered advice, it's all been very helpful.
I've got about as much heat back in the problem rads as there was before I started changing valves by using a combination of the suggested techniques.
I think the problem mainly lies with undersized pipework so will take a stab at replacing the 10mm with 15mm in the warmer months.
Does anybody see any benefit to using something bigger than 15mm when that's what I'm going to be connecting it to?

Good plan, when it warms up get some dosh ready come back on and we will be pleased to help you, thanks for getting back. Rob Foster aka centralheatking

 

[Ivan Android]

Update: In the Summer I swapped out the 10mm with 15mm.
I had to surface mount the new pipes to the wall as I didn't fancy attempting to squeeze long lengths of 15mm down between the wall and the plasterboard. I covered them up with Talon double pipe covers and as the wall is white they look just fine.

It still took a few weeks for an airlock to work its way out of the system so I was a bit downhearted by the fact that the rads were not warming up much more than they had previously. Now though they are scorching, so much so that I think I'm going to need to reduce the flow a bit.

Thanks to all who got involved in this thread. The various comments and suggestions gave me the confidence that swapping out the 10mm pipe was the way to go.