Draining a sealed system?

Neil_Sedaka

I have a wall mounted combi gas boiler (at head height) and need to replace the pressure relief valve inside, as it drips constantly.

Anyone know the best way to drain down the system for this?

Thanks.

crosstownk

You will need to locate the drain off tap. Then open it, attach a hose to it then go upstairs and open a couple of radiator bleed valves and it should drain perfectly for you.

Pataman

First turn off the boiler, then shut off the water supply to the system otherwise all you will be doing is flushing the system. Have some rust inhibitor ready to put back into the system when you are filling it. Have a small bottle with a narrow spout, and pour it into a rad before you put the water back on, and it should work its way through the system.

Reyman

Draining it is easy.

Filling it again is a pain cause you'll most likely get air locks.

I've never really figured out how to stop them but maybe somone else here knows more on this than me.

crosstownk

Air locks can take weeks or months to completely erradicate. If your pressure drops rather quickly then you may have a leak.

Neil_Sedaka

Thanks for all the replies

Where "should" I expect to find the drain off valve?
If I don't have one, will I have to drain from a downstairs rad? anyone ever done this?

Thanks.

Litcagral

Often located in the kitchen radiator (for ease of access to back door for hose).

crosstownk

Wherever it is it should be lower than the bottom of you lowest rad. Just try follow the pipework. Often they are in the weirdest places especially if the heating was retro fitted.

Reyman

There's no drain point on my heating system. Yours could be the same

You might have to open a radiator pipe at the lowest point and drain it 95% that way

Pataman

If you can get at the back of the system there will be a safety valve that opens if too much pressure builds up in the system. Turn this to drop the system.

crosstownk

Pataman wrote:

If you can get at the back of the system there will be a safety valve that opens if too much pressure builds up in the system. Turn this to drop the system.

Absolutely...........the only way if you cant find the drain tap.

It might be an idea to fit a drain so you know for the future.

JamesM

Neil_Sedaka wrote:

I have a wall mounted combi gas boiler (at head height) and need to replace the pressure relief valve inside, as it drips constantly.

Anyone know the best way to drain down the system for this?

Thanks.

Is it the safety valve that's leaking ? Is the pressure too high or is the seal faulty ? If the seal is faulty, maybe you can just screw another safety valve into the first. That should stop your leak without draining the system.

Neil_Sedaka

Yeah, the safety valve (pressure relief valve) is leaking, I'm guessing it's the seal.

Have to pressurise the system to 1 Bar every day (sometimes more often)
I have a fairly constant drip from the safety valve into the garden.

If I give the safety valve a twist and bring the pressure to 0 Bar, would I be safe enough to remove the valve from the boiler or will I still get a lot of water coming through?

Thanks again for all your help.

Pataman

JamesM wrote:

Is it the safety valve that's leaking ? Is the pressure too high or is the seal faulty ? If the seal is faulty, maybe you can just screw another safety valve into the first. That should stop your leak without draining the system.

Dont think that would be allowed.

JamesM

Pataman wrote:

Dont think that would be allowed.

I'm not argueing with you, but can you explain why ?
I know that it is done quite a lot.
If the pressure will release one valve, will it not lift the other - or are we talking about needing double the pressure to lift 2 valves ?
Jim.

JamesM

Neil_Sedaka wrote:

If I give the safety valve a twist and bring the pressure to 0 Bar, would I be safe enough to remove the valve from the boiler or will I still get a lot of water coming through?
Thanks again for all your help.

If you twist the valve and very little water comes out that will be the same as if you take off the valve - so you can do it.
Turn off the fill valve and all the upstairs valves, and if very little water comes from the safety valve, go for it. Have the new valve ready to fit with PTFE tape already on it, and go for it.
Jim.

Neil_Sedaka

When you say "the upstairs valves" do you mean both sides of the rads?
Don't want a deluge as there are lots of wires just below the relief valve on the boiler.

Thanks.

JamesM

Neil_Sedaka wrote:

When you say "the upstairs valves" do you mean both sides of the rads?
Don't want a deluge as there are lots of wires just below the relief valve on the boiler.
Thanks.

No water will come from the downstairs rads because they are lower than the boiler. You are probably better off closing both valves on the upstairs rads. Sometimes you will get away without turning off upstairs valves, but it is better to be sure. Once the fill valve is off and the rad valves are off, then there is only the small amount of water in the pipes left. If a bit of water comes out of the safety valve when you twist it, and then it stops, then you are safe enough taking it off.
Jim.

Neil_Sedaka

Cheers Jim, will give it a go