Replacing a TRV with a straight valve on towel radiator

[boronet]

Hi folks,

I'm hoping for a helping hand here. My towel radiator has stopped heating up. Tried bleeding and then removal with a wash through (lots of black gunge expelled). Then re-fitted but hardly any difference. So noted the negatives about TRVs and thought it might be stuck.

So I've bought a 15mm straight valve but it has no flow arrow or instructions and I wondered if there is a right and wrong way up to fit it. One side has a small diameter hole whilst on the other I can see the valve opening or closing. It is to be fitted on the exit side of the radiator.

Thanks in advance for any help.

 

[PlumbBobBob]

if it is a normal straight valve you will be able to see that one end should be smaller on the thread than the other. the smaller end will be for the compression fitting on the pipe coming up from the floor, the larger will be to connect onto the radiator unless you have one of those trvs that have small threads both ends in which case you need to change the part that goes into the radiator.

 

[Paulus]

There is no right or wrong way, the water flows the same whichever way you fit it.

 

[PlumbBobBob]

basically whichever way it fits it will work but ideally with small hole towards pipe away from radiator can you put a picture on?

 

[boronet]

Thanks guys for the replies earlier. Well I've got good flow through the towel rail when removed and it's now re-fitted and all the system has been bled with the heating off inc the towel rail. Central heating system back on and once again everything EXCEPT the towel rail is red hot.

The system is a gravity feed - not a combi or back boiler. I've run out of ideas now. Does anyone have another suggestion I can try? Thanks again.

 

[WaterTight]

Have you got good flow from feed and return?

Does either pipe get hot at all?

 

[boronet]

Have you got good flow from feed and return?

Does either pipe get hot at all?

The towel rad has been installed for about 6 years and had previously worked well. When the rad first stopped heating up the inlet pipe was hot but only the bottom corner of the rad got warm. The top and the other side was very cool. I've now flushed out the rad twice and re-fitted but now the inlet and outlet feed pipes are cold.

I checked the new valve for water flow before fitting. I didn't know how I could check the flow from the feed pipes because I'd drained down the system and removed the valves, so any attempt to turn the water supply back on would have produced an instant flood wouldn't it?

When the heating is off if I open the bleed valve there is instant water. I did try opening the bleed screw when the heating was on on a few occasions and no water came out at all, even after 15 minutes. Is this a clue?

 

[WHPES]

Sounds like you are airlocked. SHut all the other radiators off and turn on the heating.

Also check that the towl rail is connected to the heating circuit and not the hot water circuit as they sometimes are.

 

[PlumbBobBob]

could be. perhaps there is a blockage in the pipework caused inadvertedly when you drained down

 

[boronet]

Sounds like you are airlocked. SHut all the other radiators off and turn on the heating.

Also check that the towl rail is connected to the heating circuit and not the hot water circuit as they sometimes are.

OK, I don't know how it's plumbed but it looks like I'll be taking up floorboards then? I have tried shutting off all the other rads (which are fine BTW) and leaving this one on. Little or no difference though.

The air lock comment sounds a possibility. When I removed the rad (both times) after draining the system down there was gurgling as I cracked off the valve nuts and a rush of water. Thinking back, on the first occasion when I re-fitted it and it wasn't getting hot, I'd bled it and it was full. However, I just started to loosen the nut on the inlet side and there was a rush of water into the rad which instantly heated to almost half way but then stopped there as I tightened the nut.

Does that make any sense?

 

[Nat]

Unless the trv is bi-directional it does matter which side it goes on.

 

[WHPES]

Sounds like an airlock. Shut the valves then crack open the nut on the other side next. Try to clear it first before you do anything else.

 

[boronet]

Thanks for the suggestions. WHPES - I'll try the 'out' side as you suggest. So that's the nut on the radiator side of the valve? And if the feed side valve is closed will cracking that nut drag water through and expel the airlock?

From what has been posted it appears that when water first appears at the bleed valve it might not prove that all the air is out. Leaving it open for longer can solve the problem..?