Leaking TRV - question re 'tighten hex nut'

22 Mar 2014
Reaction score
United Kingdom
Hi all.

I've identified a leaking TRV on a downstairs rad (but not before the carpet was wet long enough to start to smell mouldy, ick). Googled a fair bit because plumbing's not really my thing and I don't really want to get in to draining down the system.

It's a sealed system, combi boiler.

TRV is leaking from around the pin. Still functions how it should but it's clearly a reasonable leak going on to have made such a big area of carpet so wet (about a square foot). Had the head of the TRV off before to fix sticking pins/valves - this being one that had previously stuck. Didn't use WD40 - smeared a bit of silicon grease on the pin when I freed it off (just by pushing it in/out carefully) back then.

As I said, I know to change the valve I'm looking at having to drain system, and no wish to get in to doign that, but elsewhere here I saw advice to tighten the hex nut the pin goes through.

I can see TWO hex nuts, not sure which I should be tightening. The upper one just spins freely it seems, made of plastic? Lower one is metal, and slightly bigger than the plastic one at the top of the valve.

Which of these hex nuts should I be tweaking? Photo attached...

Thanks! View media item 74942
Sponsored Links
Best to replace it.

As you got a sealed system, should be a easy job, drain down just enough to reduce pressure, close valve on other side of radiator, undo nuts on defect TRV and replace it. The vacuum will stop water coming out if you are quick enough. Repressure when done.

Agree with stardanny. Better to replace the trv. Although You'll have to isolate the boiler or close the auto air vent on your combi to create a vacuum. Sometimes the auto air vent is accessable without removing the combustion chamber cover. (Depends on the make/model of the combi) If you can't access the auto air vent without disturbing any case seals youll have to turn the isolation valves off to the boiler (not recommended because they can leak)
Thanks, ack.

Ho hum.

The combi's got isolation valves on it, and I can take the cover off the boiler easy as pie and find the auto air valve, but not sure I really trust it all to create the needed vacuum to stop water ****ing out from the pipe :/

Is 4" of exposed pipe between carpet and bottom nut of the valve (where it clamps onto the pipe) enough to use that funky spray-on freeze stuff?
Sponsored Links
Tighten the AAV, read the FAQ's on checking the expansion vessel, tighten down the other rad valve and replace the valve....should take under 1/2 hour. Draining down a whole system....can't remember the last time I did that :)

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local