One radiator won't turn off - should I replace valve?

[parakeet]

My kitchen radiator is filling with hot water despite my TRV being set to 0. It's blazing at maximum.

This goes for the rad when I try two separate TRVs I have tried, which happen to be...

• Basic programmable Bluetooth one that uses a motorised push-pin.
• Old basic TRV with settings 0-5.

On removal of TRV head, I can manually make the valve pin go up and down. Not loads, but I'm not sure how much it should.

Some facts and attempted diagnoses...

• Logic combi boiler is new, was installed in February 2022, replacing old boiler.
• I removed and returned the programmable valve head in September to reset it/changed batteries for the winter.
• Last month, I also attempted to bleed the rads and repressurised the boiler a bit.
• Above the kitchen/utility area is a towel rail I fiddled with last month, trying to understand which of two knobs did what and how to reduce temperature.
• I have repeatedly pushed the radiator valve pin up and down manually to check for movement, in case something there was stuck.
• I have checked that the push-in of the programmable TRV head with the motor does actually move up and down, and it does. I have applied WD-40 to the valve pin.
• I put the basic old valve back on, replacing the slightly fancier one, to check whether it was the initial TRV at fault. But it's still happening, with both heads on.
• The pipe on the right, without the TRV, gets hot first. That's the lockshield end, right?

Kitchen radiator is adjacent to the utility room containing boiler, both on bottom floor of a terraced house. Kitchen rad is the only one to come on without asking like this. Kitchen rad is probably the first one to get fed by the boiler - unless that honour goes to the towel rail upstairs.

It makes a hissing/water sound (ie. fully open) until I push the pin down with a finger or object, which I think closes the gate.

What's going on here?

Given the above facts, one plumbing aficionado suggested it may be the angled valve part, beneath the actuator/head, is broken - ie. although the pin pushes down, maybe the gate beneath is jammed.

So I have watched a lot of YouTube videos of plumbers replacing that part, and made notes on what to do; broadly...

• Turn off boiler.
• Isolate the radiator by closing the lockshield end (not possible at TRV end if it won't close?)
• Drain the radiator... open bleed valve. Loosen right-hand nut a little, catch any water, allowing to drain/dribble-out/slow.
• Remove upright nut... loosen the nut and stabilise the valve itself to avoid kinking.
• Set new valve to 0.
• Remove old valve... put thumb on exposed upright pipe, put new valve on quickly and hand-tighten a bit, insert to right hand pipe and hand-tighten, then tighten both nuts.
• Finish up... shut the air/bleed valve, open TRV fully, water goes in, re-open lockshield valve by equivalent number of closure turned.
• Need to close bleed valve, repressurise boiler?

I have bought a Regis 10/15mm angled TRV for £15, with the intention of replacing that part (no need for the control head) as per the instructions - if I'm feeling brave enough.

And I'm not sure if I am... I'm not a plumber.

Does it sound to you like the valve needs replacing? Or could it be something else? I've read about check/diverted valve.

 

[Deleted member 120897]

It does sound like it wants replacing, if the trv end isn’t closing then you’ll likely have to just drain the leg without control. You could try a decorators cap and fully screw down onto the trv pin.

 

[parakeet]

It does sound like it wants replacing, if the trv end isn’t closing then you’ll likely have to just drain the leg without control. You could try a decorators cap and fully screw down onto the trv pin.

Actually, if it's broken beneath the pin, maybe that wouldn't help?
I'm already able to push the pin down with my thumb or a heavy object.

?

 

[Ben-gee]

Has it worked correctly in the past?

If so then it needs replacing, if not then it may not be bi-directional and could work if you swap it with the lockshield.

In your description, you will not isolate the radiator by only shutting the lockshield side.

 

[parakeet]

Has it worked correctly in the past?

If so then it needs replacing, if not then it may not be bi-directional and could work if you swap it with the lockshield.

It worked fine until a couple of weeks ago.

In your description, you will not isolate the radiator by only shutting the lockshield side.

Thanks, I learned that.

So, at best, I'll get some water coming from the TRV end (to drain); at worst, a horrible spurt, right?

 

[Ben-gee]

As your system is pressurised as long as you only have one outlet open you can drain off some water and then it will hold on a vacuum.
In your case use the faulty trv as this can’t be shut..
I stress that you may only have one thing open- so you need to check for and close any automatic air vents first.
Alternatively just drain the entire system, this is safer method, but I personally would change a single cave on a vacuum as it is quicker and you don’t lose the inhibitor from the system.

 

[parakeet]

Closing the loop...
I replaced the valve body and, yes, now the radiator will turn off.
Only thing is, now my radiators are generally patchy. I guess I didn't achieve an air lock / drained most of the system out through that rad... I think I need to bleed them.