Cold Radiators

[Dantc]

Hi,

I have a puzzling problem. We moved to a house middle of last year with a air source heatpump and radiators with TRVs, house is 3 years old. The heating has not really been called upon much until the winter. We have 2 zones, upstairs and downstairs.

Everything fine upstairs, all radiators working fine. Downstairs was problematic, which I finally identified was a faulty zone valve head, which I replaced and all appeared to be working. However I have 2 radiators downstairs which never get hot, they don't even get tepid. Completely stone cold.

I have bled all the radiators, the pressure at the storage unit is 1 bar. I tried removing the TRV and checking the pin was not stuck underneath. I checked the LS valve was open. I have also completely removed one of the radiators and flushed through the radiator in the garden. While I had the radiator off I opened the LS valve and water under some pressure was coming out, repeated on the other side by opening the TRV valve and had a similar result. I've tried closing the other radiators, still no heat and finally tried balancing the other radiators using guidance online, with a lower temperature gradient on either side (5C) of the working radiators to account for lower teperature feed from the heat pump system.

Admittedly I didn't release lots of water from either the TRV or LS side when I had the radiator off but it seemed to flow quite well.

I am now at a loss, Any ideas?

 

[motorbiking]

When you flushed the radiator did water come out from one end to the other? Have you tried closing all other radiators to see if they get warm?

 

[Dantc]

Hi,

Yes I connected a hose to one side and water was free flowing through the radiator, also blocked the exit hole and the radiator filled up completely and out of the bleed hole (left open).

Tried closing the other radiators and still no heat.

It's a puzzle, I did notice when adjusting the LS valve on other radiators nearby that the input pipe on the TRV side of of the cold radiator did just get very slightly warm before cooling again.

 

[motorbiking]

Its not a one pipe system is it?

 

[45yearsagasman]

Its not a one pipe system is it?

Probably not, as the house is 3 yrs old.

 

[motorbiking]

It could be that the installer put the rads in series.

 

[Notch7]

I’ve seen new builds with radiators not even connected to the central heating - just tails sticking down into the floor.

It wouldn’t surprise me if it’s plumbed incorrectly.

 

[Dantc]

Hi, Thanks for the replies, quick update.

I decided to have a go with the other cold radiator on the weekend. Drained radiator and removed from wall. Flushed the radiator completely with hose in one side, water flowed out the other side, removed bleed screw and blocked exit hole, hose pipe still running, radiator filled up completely, unblocked exit hole and radiator emptied very quickly.

Connect short length of hose to pipe with TRV, opened TRV and water came out of hose under pressure, released quite a few litres and closed TRV, moved hose to LS valve side and repeated with same results.

Refitted radiator, TRV and LS valve closed. Opened bleed screw, opened TRV and radiator started filling. Closed TRV, opened LS valve, radiator continued to fill. Opened TRV again and allowed radiator to fill, closed bleed.

End result is the same, all radiators except these two get hot, these two radiators remain completely cold. Also the water in the system is very clean, no sign of sludge or dark water.

So I am at a complete loss, the radiators are definitely connected to the central heating pipes, no indications of air in the pipes. My only working theories are that when the system was put in they have connected both sides of the radiator to the outward hot water feed or both sides to the return water pipes, but no idea how I diagnose that without ripping into the walls and floor.

The other possibility is I have some kind of pressure issue on the return side, I did notice that the water pressure on the LS valve side is definitely higher than the TRV side, With the TRV open I could with some pressure block the pipe to stop the flow, the pressure was too high on the LS valve side to stop the flow with my hand. Looking at the other radiators which work, the TRVs are all on the input side based on which side of the radiator starts getting hot first. It's a closed system with a fill loop and set to about 1 bar.

 

[oldbutnotdead]

Good work on the pipe testing. Have you tried it when the system is hot- this might help with your faultfinding. System warm.
Remove rad.
Run from trv end, see if water gets hot, how long it takes, how hot it gets. Repeat for lockshield end.
Don't forget to top up with inhibitor after all this fresh water fun