Discuss I've made my heating system worse! in the Plumbing Jobs | The Job-board area at PlumbersForums.net

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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?

IMG_20190106_145401.jpg
 
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.
 
@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?
 
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?
 

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