How to remove a TRV/ Lockshield valve without bleeding whole system

[ukjules]

I had another post but wanted to start a new one as this may help others ....

I have a radiator that I want to replace the TRV Valve and be useful to know if there is a difference for the Lockshield valve replacement.

I want to do this and not drain the whole system (although I have the tools to do that and knowledge how to re pressurise)
(I have recently removed , replaced a radiator , bled rad and depressurised)

Task:
15mm pipes , Combi boiler , Radiator at bottom of house, Has TRV and Lockshield valves.

Method / How:
- If I turn off all other valves TRV and LS can I if quick swap out a valve ? If I had a plumbtub to catch water ? I really don't want to drain system (I fear that for some reason)
- Is there a bung I can use to stick in the 15mm pipe or rad end briefly to help ?

The question is how can I do this easily ?
Also if the rad had 8mm microbore pipes are there any precautions taking time ff that type of valve ?

I'd so appreciate your thoughts !

 

[denso13]

Turn off all the other radiators and the TRV on the one you are changing. Open the lockshield and drain into a bucket, you shouldn't lose much. Then change valve and refill/bleed.

 

[ukjules]

Would I have to be quick ? As the water in the 15mm pipe be live ? I mean it will be on within 3 seconds but is that ok with the pressure of all the water in system ?

 

[denso13]

Would I have to be quick ? As the water in the 15mm pipe be live ?

No, let it all drain into a bucket, there will be no water left running.

 

[ukjules]

I'm not quite on this ...
Agree the water in the radiator will be in the bucket.
But when I remove the valve from the 15mm pipe it has a house if water above it ?

 

[denso13]

But when I remove the valve from the 15mm pipe it has a house if water above it ?

You won't get much out of the valve as all the other radiators will be off. Just some out of the pipework, shouldn't be a lot.

 

[ukjules]

Ok so with the valve off the rad , rad now empty , all other rads off whipping off the valve off 15mm pipe and putting a new one on should be ok (if have towels etc etc at the ready) as there will be some .

Ok thanks so much as I don't want to drain the system.

Question
If on a micro bore pipe which I may come across are there any preemptive steps to take when undoing valves ?
Bar holding them tight so not to twist etc etc

 

[denso13]

all other rads off whipping off the valve off 15mm pipe and putting a new one on should be ok (if have towels etc etc at the ready) as there will be some .

You won't need any whipping, open the valve, run it into a bucket until it stops. There will be no rush.

If on a micro bore pipe which I may come across are there any preemptive steps to take when undoing valves ?
Bar holding them tight so not to twist etc etc

Simply that, don't allow any twisting etc.

 

[ukjules]

But but but
If I just open valve which is still on 15mm pipe but off rad I'm basically draining the system am I not ?

 

[denso13]

If I just open valve which is still on 15mm pipe but off rad I'm basically draining the system am I not ?

How are you draining the other rads if they are switched off? You might drain a bit of pipework but not much more. Think also of putting your finger over the end of a straw full of water, when you hold it up, no water comes out.

It's a sealed system, no air can enter to let water out.

 

[ukjules]

I almost get it.

All I want to do is remove a TRV or lockshield valve from a 7 rad Combi boiler system.
The radiator is at the bottom of house.

Tell me where I am.wrong with these steps:
Boiler off.
All rads - tvr and lockshield valve set to off to help with water coming out of rad I'm working on ? Is this right ?
I then drain the rad I'm working on.
So say one valve is on but turned off the other I'm gonna remove
Remove from rad
That leaves it on the 15mm pipe.

How do I get it off without draining the system ? I am afraid of a house full of water coming out ?

Sk from that point - where are we at ?

 

[denso13]

That leaves it on the 15mm pipe.

Then open it and let it run into a bucket. You don't take the valve off the pipework until the water stops running. No risk.

 

[Elkato531]

If you have a combi boiler, there will be an auto air vent within the boiler which will allow air into the system and water to then flow out of an open pipe if it is lower in the system. If you close the flow and return valves on the boiler you isolate both the auto air vent and the expansion vessel (which is a pressure reservoir). This will allow the system to go to vacuum very quickly so that valves can be replaced with minimal water loss.
The risk is that on some older boilers, the flow and return valves are very flaky and are very likely to leak once re opened. What boiler do you have? There are many that I would always trust and some that I would never even sneeze within 10 feet of.

 

[ukjules]

As the title says jndjnt want to bleeding removing all water from system ...

 

[denso13]

As the title says jndjnt want to bleeding removing all water from system ...

Just try what I suggested, if you find too much water is flowing from the open valve, just close it again. There is no risk.