REPLACING A VERY OLD TRV

sandramcl

The black plastic ring with screw has disintegrated on my old TRV and fallen off( I think Danfoss).  I would like to replace with a new TRV without draining the system. Cn anyone help please.

molerat

If it is purely the head, which I suspect it is as you mention "black plastic screw",  then that is replaceable.  If it is part of the valve itself then draining down would be the only way.  Can you link to a photo ? One of these ?

FreeBear

Whilst you could use a pipe freezing kit on the pipe below the TRV, the radiator would still need to be drained once the lockshield has been closed right down. Going to be messy though, and the radiator would need balancing again.

To be honest, much easier to drain the whole system down - It gives you the opportunity to add fresh corrosion inhibitor when refilling. Whilst the system is drained, you have the chance to replace other TRVs that might be suspect along with any radiators that are starting to show their age (rusting along the bottom edge for example).

With an old system, I'd be tempted to add a flushing agent, run the system up to temperature, and then drain down. Perhaps even connect a hose pipe up to another drain point and flush out all the muck. Ideal opportunity to add a magnetic filter if you don't already have one.

Lorian

All of the RA series heads either have a twist collar or an Allen key grub screw holding the head on the valve. Danfoss TRV valves themselves are very reliable in my experience. I'm using 25 year old RA valves. No draining down required. The aero heads are the fastest operating and look more modern.

sheenas

Turn off the boiler, close down all radiator valves and purchase a foldable bucket from Amazon. You can get a 12l one for about £7. Towel on the floor and carefully loosen a convenient bolt and drain into bucket. You get quite a bit of water, but I say less than a bucket full. If you matched the valve length and height carefully then it’s a straight replacement. Use ptfe tape on the olive and don’t over tighten. Plenty of utube vids on this job. 

Reed_Richards

It's the same valve with a different valve head whether it's a TRV or just a manual adjustment.  Before you get too caught up with advice on replacing the valve make sure that it's not just the valve head  that needs to be replaced.  Because that's just a matter of unscrewing the old one and replacing it with a new one. 

FreeBear

Reed_Richards said:

It's the same valve with a different valve head whether it's a TRV or just a manual adjustment.  Before you get too caught up with advice on replacing the valve make sure that it's not just the valve head  that needs to be replaced.  Because that's just a matter of unscrewing the old one and replacing it with a new one. 

Agreed, if it is just the head, no need to drain the system.

Still. Doesn't hurt to add some corrosion inhibitor, although, on a sealed system, it is not that easy.

sandramcl

Thank you for all the responses.  I think it is only the head and black plastic ring with screw that needs replacing but I am happy and would probably prefer to use new head (not sure if that is the terminology.  I would prefer not to have to drain my system as that sees a bit extreme.  My problem is the new heads have a screw on attachment whereas my old Danfoss has a black ring to tighten.  See pic below.

FreeBear

Looks like you can get replacement heads -> https://www.amazon.co.uk/Heimeier-Thermostat-9700-24-500-Connection-Danfoss/dp/B004VR9N38 - Check the diameter of the mounting ring before you order.

You wouldn't need to drain the system down to replace the head.

molerat

Def looks like a 26mm RA/VL.  You also need to check the pin is moving freely once the head is off.  Genuine Danfoss occasionally come up cheap on Ebay - got a couple last week for £27 for the 2. Once one breaks more are sure to follow.  https://www.amazon.co.uk/Danfoss-Thermostatic-Radiator-Gas-Filled-Sensor/dp/B0928Z2C28

Lorian

Danfoss ra2910 has a grub screw to tighten if you'd rather not have the twist ring.