Swapping radiator valves between two rads

[DerekPCB]

In the linked photos you can see two radiators, one with a static valve and the other a TRV (with head removed). I need to swap the two valves. The third photo is the lock shield at the bottom of each rad.

What are the correct steps to swap these two joints without hopefully having to flush an entire system? If I undo the nut of the valve at the top, and disconnect the hose, should I expect water to gush out?

Note, I have a district heating system (external heat source feeds my property hot water). I could turn off the HIU and close the 6 inlet/outlet valves to it, but rather not as last time service engineer found it near impossible to open and close them.

 

[Madrab]

Removing a valve in the top of a rad is probably the easiest way to do things. Your trouble is the district heating. You do need to isolate your system from the main. So that does mean shutting off the feeds on the HIU.

Once that's done then you would shut off all the rads at their TRV valves, open up the bleed valves on the rads you want to remove the valve from and release the pressure until the water stops running. Then it's just a case of loosening the nuts and removing the valves. You will lose a little water from each so have something underneath to catch the water released but it shouldn't be a huge amount.

Why are you swapping them? Cant think of a reason why that would be needed and why not just replace?

 

[DerekPCB]

So that does mean shutting off the feeds on the HIU.

If I turn off all the other rads in the property, and switch off the HIU, is that not enough? Like I said, it near killed the engineer when he turned the inlet/outlet valves coming to the HIU last time. That is another question for another time. Doesn't seem to be right such force is needed, unless it's due to pressure or something. I might just give it a go as you suggested. Just need to find correct wrench size when I pop out.

Why are you swapping them? Cant think of a reason why that would be needed and why not just replace?

The installers got the valve types wrong when the house was built. They put a static valve in my living room, and the TRV in the hallway as pictured. I read elsewhere that it makes sense for one rad in each zone to be static (for safety?), but it's normally in hallways. Living spaces should be TRVs like all my other rads. Then actually why I am doing this is so that I can install a smart TRV in the living room, but need the correct joint to begin with.

 

[Madrab]

If I turn off all the other rads in the property, and switch off the HIU, is that not enough?

The trouble you have is that if the HIU isn't isolated from the district's wet system @ the primary valves, all you would be doing when taking off your rad valves would be releasing all the pressure from the local system, if that system is still connected to the 'district' system, then all that pressure would be released too, if you see what I mean. There's no way around that I'm afraid. probably why the previous trade had such a problem as they must be turned off to service anything locally.

As far as one rad needing to be without a TRV and just manual lockshields, then only where a fixed room thermostat is present, that's then just to stop one thermostatic control fighting the other. As far as safety is concerned then no, I'm afraid you've been misinformed there, no requirement for any safety reasons I could think of in your type of setup.

 

[DerekPCB]

probably why the previous trade had such a problem as they must be turned off to service anything locally.

I'm happy to try it myself. It's 6 primary valves next to the HIU. Can you think why they would be so difficult to turn on/off? Could it be there is something else that needs to be done first e.g. turn off mains water at stopcock? There is also what looks like a waste water/return pipe back from the HIU to the ground. That though has a massive lever to turn the valve so easy to use. Perhaps I need to spray some WD40 on the valve in case the valve is just stiff.

As far as one rad needing to be without a TRV and just manual lockshields, then only where a fixed room thermostat is present, that's then just to stop one thermostatic control fighting the other. As far as safety is concerned then no, I'm afraid you've been misinformed there, no requirement for any safety reasons I could think of in your type of setup.

I have two zones. One zone has all rads on TRVs i.e. with twist numbers except for the ground floor radiator in the hallway which still has a twist knob valve but not numbers. The hallway is where the wired fixed thermostat is. Second zone again has TRVs on all rads, except this time, the living room has the manual twist valve, and the landing radiator has a TRV. The landing is where the second wired thermostat is located, hence why I think that is where the manual valve radiator should have been, but incorrectly put in the living room.

One quick question. When removing the valve and refitting, do I need PTFE tape or some sort of compound?

 

[Madrab]

I'm happy to try it myself. It's 6 primary valves next to the HIU

Actually, what am I saying, thinking again - can you give me the make model of the HUI? It will probably have a primary HEX that will be in effect isolated from your local system, if that's the case then you'll be fine and no main system valves need to be shut off

If so, all you'll need to do is shut down the rads, vent the system pressure at the vents on the rads and then as I suggested above.

The landing is where the second wired thermostat is located, hence why I think that is where the manual valve radiator should have been, but incorrectly put in the living room

Spot on.

 

[DerekPCB]

As far as one rad needing to be without a TRV and just manual lockshields, then only where a fixed room thermostat is present, that's then just to stop one thermostatic control fighting the other.

Can you explain this in layman's terms. Why would that be a problem if in the landing there was a TRV and the wall thermostat. Doesn't the main thermostat just monitor ambient temperature, when it hits it's desired number, it turns off, causing hot water to stop flowing through the rad/TRV. In what situation could they be "fighting"?

 

[Madrab]

So the hard wired wall thermostat controls the call for heat in the whole zone, not just that rads space, so if you have a TRV on that rad where the stat is and that TRV was that was turned down, then that rad could never heat that space up properly, that wall stat would never reach it's set temp and the heat source/pump would run constantly, not very efficient nor economic.
The whole point of a wall stat is usually to get the coolest room and all the others up to a set temp and and then switch off the boiler. It can't do that if it has to compete against a TRV that only control that one rad

 

[DerekPCB]

Finally had time yesterday to swap them out thanks to your help and the faq guide - https://www.diynot.com/wiki/Plumbing:faq12. It took about 30mins because I was being cautious. I was a little concerned at first because draining water using the bleed valve was not working (too slow), and when I took the inlet pipe off one rad, water was gushing but quickly stopped.
Also, I was expecting to leave a part of the valve connecter (where PTFE tape is used) left attached to the rad, and unscew the bolt you can see in the photos on the valve itself, but I think it's all one piece. So I undid the valve from the rad, PTFE included, and attached it to the other rad.