I've made my heating system worse!

[Ivan Android]

Hi all I have an issue with a couple of radiators that I'm hoping I can get some expert eyes on to help diagnose.

I recently drained down the heating system, fitted some TRVs and then refilled and since then have two problem rads. They are both in a single storey extension to the side of the property.

The system is a pretty bog-standard gravity fed type with the cylinder, pump, 2 port valve etc in a first-floor airing cupboard. The two problem rads appear to be fed via a loop near this cupboard. This loop comes into the loft space of the extension, drops down in to the 2 rads and then goes back in to the main house. I've attached a photo to illustrate the connections.

Here's the bit I don't understand. If I open up only the return valve (empty rad, bleed valve shut) on rad B water comes out, if I open up only the feed valve on rad B water does not come out unless I open up both valves on rad A. This seems counter-intuitive to me as the flow to rad B as far as I can see is not dependent on rad A.

I suspect the issue is with an airlock somewhere but don't have the experience or skill set to diagnose this. I've tried attaching a hose to both rads and gently applying mains water pressure to each for a short period of time and I'm reasonable confident that it didn't encounter any blockages.
I should add that I've emptied/refilled the system partially a few times recently as I did a few valves over the course of a few days and after fitting the TRV to rad B there was a supply of hot water flowing through it so I don't think my fitting is the cause.

The feed and return are a mixture of plastic and copper 15mm reducing down to 10mm microbore where they drop down the walls into the rads.

Can anybody help?

 

[Riley]

How big are the rads and did they heat well before?

 

[Aire]

When filling up did you have any issues filling the radiators? Did they all bleed properly? If you had no issues filling and everything ran fine before then it's probably an airlock. Run your heating. Turn off all your rads in the house and leave the ones in the extension open. If there's an airlock that should force it out.

 

[Ivan Android]

@Riley 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

 

[Ivan Android]

@Craig Watson No, there were no issues filling up. Have tried what you suggested along with turning up the pump to its highest setting. They got marginally warmer but only by a very small amount. The feed at both rads is hot, there's just no flow through them for some reason.
I put some Fernox F3 in at the weekend. I'm thinking about trying to close the other rads again. Can't hurt?

 

[Aire]

The pipes in the pic, are they in a roof space?

 

[Riley]

I’d say maybe pipework undersized

 

[Ivan Android]

The pipes in the pic, are they in a roof space?

Yes

 

[Ivan Android]

I’d say maybe pipework undersized

Would make sense as they were never as warm as the others. I can't say for sure though as we've only lived here since July so haven't had that much experience of the system in full flow.

However.. To play Devils advocate.. If that's the case wouldn't it be the case that they would work fine with the rest of the rads closed?

 

[Aire]

How do the pipes in the loft connect into the heating system?

 

[Aire]

However.. To play Devils advocate.. If that's the case wouldn't it be the case that they would work fine with the rest of the rads closed?

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.

 

[Ivan Android]

How do the pipes in the loft connect into the heating system?

They tee off somewhere on the first floor. There seems to be a dedicated feed and supply that only goes to these 2 rads, I think it's connected near to the pump but I could be wrong. I'd estimate there's a run of about 5-6 meters of 15mm pipe on the first floor before the connections in the picture I posted.

 

[Ivan Android]

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.

Interesting. At least part of the system is 22mm, I have seen this when fixing squeaky floorboards. I assume this would only compound the issue?

 

[Ivan Android]

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.

Do you have any suggestions on locating or removing the airlock?

 

[Aire]

So the loft these pipes are in is a ground floor extention? When you turned all other radiators off, did you switch off the hot water at the programmer?

 

[Riley]

Would make sense as they were never as warm as the others. I can't say for sure though as we've only lived here since July so haven't had that much experience of the system in full flow.

However.. To play Devils advocate.. If that's the case wouldn't it be the case that they would work fine with the rest of the rads closed?

No as the smaller bore pipe can only carry so much heat

 

[Ivan Android]

So the loft these pipes are in is a ground floor extention? When you turned all other radiators off, did you switch off the hot water at the programmer?

Darn it. Will do now

 

[Ivan Android]

I've closed off all of the rads apart from the problem ones (and the hot water) and there is heat there.... More than earlier on today but much less than there has been on it's best day

 

[Aire]

Keep turning the pump on and off in cycles of 30 seconds to try dislodge the air, do this for a about 5 - 10 minutes

 

[Riley]

Well yes

 

[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?