Completely cold rad - out of ideas, any thoughts?

Phibsboro

Combi boiler system, 2 years old, underfloor downstairs, 4 rads upstairs. The rad in the guest bedroom, where the boiler is, is staying completely cold while the rest heat up. What I've tried so far:

• Replaced both the lockshield and trv.
• Took the bleed valve off and attached a hose - neither side really flowed, which is confusing! Made me think the whole rad might be bunged up, so...
• Took the rad off and brought it out to the garden to flush. Very black initially, ran it through until it was clear.

Put the rad back on and to my astonishment it still wouldn't heat! What on earth is going on?

Some other observations:

• What I think is the flow pipe (which has the TRV on it) remains cold, while the return pipe will eventually get warm (a good few minutes after the rest of the rads are hot)
• If I bleed the rad excessively the flow pipe does heat up and I can feel heat coming into the rad on that side, just the "knuckle" that is on the underneath at the side.

Could the flow pipe be blocked in some way? Would an unbalanced system just refuse to flown through the last (or first, I'm not sure which but I assume it is one or the other given the boiler is a metre away) rad like this?

I am guessing a plumber is next but I've done so much DIY on this one that I'd love to solve it myself. Any help would be appreciated.

cruizer101

Could you try close off all the other rads and see if it warms up then.

NickNickleby

Messy, but....

If you remove and drain the rad again - presumably the TRV and lock-shield are full locked down at this stage. THen refit the rad, but open only the TRV and see does the rad fill. Might give you a further pointer.

Did it EVER work?

Phibsboro

It doesn't heat at all with the other three rads turned off. Someone who stayed in the room last winter swears it used to work - I have my doubts!

Re turning on the trv with the flow closed I'm not sure what that tells me? When I put it back on I opened both, trv first. Some gurgling when the trv opened then nothing when the lockshield opened. I bled out all the air and some residual heat did flow in from the trv side but presumably just to the point that the water replaced the air. After that no heat and trv pipe cold. I imagine that if I flush again and put it back empty then nothing really would happen with just trv open until I bleed it?

Wearb

Are you getting a good flow of water out of the bleed screw? What pressure is the gauge reading?

Danno

Is there a setting on the pump near the boiler? Marked I, II, III?

NickNickleby

https://www.boards.ie/discussion/comment/118475518#Comment_118475518

my thinking was that, when you re-fit the radiator and open just one valve, it will fill the rad - when the bleed valve is opened. However, if there's no hissing when the trv is opened, it might suggest that the pipe leading to the TRV is blocked. If there IS hissing, then close the TRV, at which point the hissing will stop. Then open the lockshield. If no hissing is heard, that suggests THAT pipe is the one that's blocked. Of course if hissing is heard on both, then there might still be a partial blocking. You can probably tell I'm no plumber, but I'm just throwing stuff out there. There's plenty of good people on here who will come up with some more useful (as in better, mine might not even be useful😅) pointers. Good luck with it.

BTW, I had a problem rad in my previous house. It was caused (I was told) by poor routing of one of the pipes to that rad. It was the flow, and it had a significant 'dip' in its length as it passed under one of those 'blocking' pieces between joists.

PJLimerick

Had similar issue in father's house when heating put on for first time after the summer. One rad cold all the time. Turned out the metal valve part of the trv pin was stuck. Remove the trv housing. A squirt of WD-40 into the metal pin fixed the rad. Spray the actual radiator valve pin and not the plastic pin in the trv housing.

Irish Steve

Based on experience here, one of more of the 19 here sticks most years, it is very possible that the valve under the TRV head is stuck, jammed in the closed position. If you take the thermostat head off the TRV, there should be a small pin under the head, in the middle of the valve. Can you press that pin down, (or in if it's mounted horizontally) and does it come back up/out again when you take the pressure off it. If it does not move, or appears to be stuck very close to the valve body, that is what has happened, it's jammed in the closed position, and needs to be freed up. Try pulling the pin up/out a little with a pair of pliers, carefully so as not to damage the pin, and see if it moves, don't pull too far, as you don't want to pull it out of the valve body, normal movement will only be of the order of 5mm or so. If you have some silicon spray or similar, that may help the process, the objective is to get to a point where the pin is above/out of the valve by around 5mm or so, and when you push it down/in, on releasing it, it comes back up/out again. Usually, it will free up quite quickly, and once it does, it will move freely in and out with very little pressure required to move it. if it's moving freely, the radiator should heat up with the thermostat head off, once it's replaced and reset, it should start operating as intended.

Phibsboro

The original TRV pin was fine but I actually replaced it and the lockshield as my first attempt to fix it.

It is a closed combi system so the pressure is set by a fill loop thingy, I have it mid green, about 1.5 bar. There definitely seems to be a good flow out of the bleed. Also, when I was changing the TRV, after doing the de-pressure the system thing, there was a surprisingly strong flow out of the pipe. I guess this is all suggesting something on the flow pipe side, though as I said that pipe is warming up somewhat once the other rads are fully hot.

I'll have look for that I, II, III thing now...

Phibsboro

Turns out the pump (which I assume is what would have the I, II, III) is built in to the boiler, a Baxi 600 combi, Looks like it is not adjustable.

NickNickleby

Just saw something on Google. Apparently its not guaranteed that you can put the TRV on either flow or return. So you should check your new TRV for that. If you're in doubt, why not just swap them and see?? (I'm a great man for the 'simple' suggestion. hahaha.).

Phibsboro

https://www.boards.ie/discussion/comment/118477159#Comment_118477159

Yes I thought thats what it might have been initially, but both the original TRV and the new one are bi directional. Also apparently the main symptom of putting an old style one-way TRV on the wrong side is just a noisy TRV, it will still work.

John.G

Just to recap/suggest.

Shut off TRV & Lockshield, open rad vent, water should stop, open TRV, are you getting water from vent, if so...not a TRV problem.

Its just possible but unlikely that the flow&return rad tails are teed into the same manifold pipe, so no circulation. another test but a little messy, mind the missuses carpet. Ensure boiler firing, again shut off TRV&lockshield, remove rad vent fully, get a bucket or similar, open say the TRV fully and let the water flow into the bucket for say exactly one minute, measure it. Do ditto with lockshield open, TRV shut, there should be very measurable different volomes of water if tails teed in properly. Found this problem 40 years ago in neighbours bedroom rad.

Phibsboro

https://www.boards.ie/discussion/comment/118478742#Comment_118478742

Definitely getting water from the vent after opening the TRV. I did the hose to vent thing again and there is a definite difference in flow between the trv side and the lockshield side. The TRV side is maybe 4 times as much water over a minute as the other side. The other side did have some flow though so not actually blocked as I was suspecting. At this stage the rad seems to be defying physics! Totally confused, time for a plumber I think. I'll update the thread with the outcome. Thanks for all the suggestions.

John.G

It just might be worth (with boiler shut down), increase the boiler pressure by topping up to say 2.2/2.4bar, with vent fully removed keep back flushing the return line while getting someone to keep that pressure topped up, you might just clear a air pocket if you flush a few buckets of water through it, I would do do likewise with other side, it certainly looks like a air lock now. If this doesn't work call in the troops.

When flushing complete return boiler pressure to normal.

Phibsboro

https://www.boards.ie/discussion/comment/118485378#Comment_118485378

So, that was interesting. I did the return first and empited out a full big tubaware container. It was a big spluterry to begin with so I thought I might be getting somewhere. Then I closed the lockshield and opened the TRV - nothing! Closed the TRV and opened the lockshield - nothing! Checked the pressure at the boiler, all fine. Eased off the hose connector at the vent and opened the TRV, water gushing out. So it looks like the hose air locked? I don't know what to make of that at all. Either way, it didn't fix the issue unfortunately.

John.G

Definitely, a airlock problem IMO, get rid of that hose connected to the vent as any air cannot escape straight out of the vent, just hold the bucket opposite/below the open vent, you have plenty of control with the valve(s).

Also ensure any zone (motorized) valve that supplies this rad is opened otherwise above no good.