Isolating hot water from Combi.

It's plumbed into next-door neighbours ;-) ? Thermostatic tap that actually had inputs for hot and cold ? Mind you, there's usually protection the input such that if one of thm cuts out, so does the other one - but such protection could only be on hot cut- off ? Now, if you also cut off water at the house stopcock and it still worked ... Simon.

Either the shut off valve is bu****ed or you've not found the right one. The latter easily checked - it should kill all the taps in the house.

By saying the one 'into the boiler' makes me think that's the one for the central heating circuit.

=A0 London SW

The arrangement is that a 22mm pipe runs right into the combi - I am assuming this is the incoming mains. T'eed off this is is the filling loop which is connected to a 15mm pipe into the combi.

I suspect that as you say, the shut-off valve may be broken.

Mark.

I think you will find the 22mm was the central heating pipe, and the 15mm was the mains water input!

Toby...

No, that 15mm pipe is the mains in. The 22mm will be part of the heating circuit.

Not a gate valve by any chance?

Ah, that sounds like the return for the central heating... what is on the other end of the filling loop? That is probably the mains. (The boiler probably has a 15mm inlet for the mains water)

Unlikely - mains is usually 15mm.

The other side of that 15mm would be connected to mains to fill it. But should be disconnected after filling.

You need to find the main stopcock for the house mains water. Usually by the front door or under the sink. Turning that off should stop the water flow immediately. Check with the kitchen cold tap.

All this assumes it actually is a combi.

=A0 London SW

Yep, deffo a combi. The 22mm pipe is on one side of the loop and the 15mm is on the other side.

I disconnected the end at the 22mm pipe, directed the loop at a bucket and opened the valve on the 15mm pipe and mains pressure water squirted into the bucket - with no change in pressure on the gauge of the combi - so I am assuming this is the mains.

Due to a bit of over-filling we had to release some pressure from the boiler - I though this could be achieved by disconnecting the 15mm end and openinng the valve at the 22mm pipe - but nothing came out. I ended up removing it from the bleed point on one of the radiators.

What is the normal way of releasing some pressure on a combi?

Thanks, Mark.

That still doesn't make sense to me. Can you list all the pipes to the boiler?

Well yes. You fill the boiler heating circuit from the mains.

Either from the boiler drain/fill valve or any bleed valve in the system. But that's not exclusive to a combi.

Filling loops have a check valve fitted, maybe its on the wrong pipe and it wont allow you to release the pressure? Opening either valve will normally get a flow of water, cold mains on one and from the CH loop on the other.

=A0 London SW

I don't recall all the pipes - I'll try and take a pic later in the week - because this is confusing me! So if I disconnected the filling loop from the main-side and opened the fill valve on the combi - would you normally expect water to come out? Or does it have some kind of check valve that allows water in, but not out?

Mark.

I'm not sure on your particular boiler. There should be a one way valve somewhere in the filling loop to prevent contaminating the mains water.

Via a drain point. Bleeding the system if there is gas in it may be enough.

The purpose of the check valve is to prevent any flow of water out of the heating circuit (and potentially into the mains supply). Some check valves have a bleed screw, but by no means all.

Maybe wrong assumption: could be gas supply or either CH flow or return.

Then the 22mm is likely to be the CH return (or possibly the flow) and the