Temporarily turning off hot water in a combination boiler system?

[Adam Funk]

I need to fix a hot tap in a sink in a relative's house (either clean out & replace the washer, or perhaps replace the tap) --- that's fine. But there's no service valve for this tap, and she has a combination boiler.

What's the correct procedure for turning off the flow of hot water from the boiler in order to cut the pipe and put a service valve in? Should there be a valve somewhere downstream of the boiler, or do I turn off the main stopcock coming in?

Thanks.

[Scott M]

There's no "correct" procedure. Just prevent the water flowing!

There's usually a valve on the cold water inlet of most combis. Otherwise just turn off the cold on the stopcock.

No need to turn the heating off either.

[Tim Watts]

Unless there is a ballvalve isolator inline with the tap, there is no standard valving - it's always house dependent.

Quite possibly.

[newshound]

Don't Combis normally have a tap on the DHW outlet? That said, turning off the main at the inlet (or the stop tap) is all that is needed. It's perfectly safe to leave the CH running with the mains stop tap turned off.

[Adam Funk]

Thanks, everybody. I do remember that her boiler has separate controls for turning the CH & hot water on & off.

[NY]

Er, are you talking about turning off the heating aspect of the boiler or turning off the water supply? I thought you were talking about replacing a tap washer, which mean tuning off the water supply to that tap (either by closing a stop vale of by turning off the rising main). Turning off the hot water control at the boiler would simply ensure the water to the tap was cold rather than hot - it wouldn't turn off the water flow itself. Maybe I've misunderstood your phrase "her boiler has separate controls for turning the CH & hot water on & off" - maybe you are referring to a tap rather than a control switch. Or maybe your system has motorised stop valves, which

*would* mean that when HW is turned off at the boiler controller, water flow was turned off.

[Adam Funk]

What I mean is this (just to clear):

1. turn the boiler control for hot water off;
2. turn off the main stopcock;
3. cut into the pipes and add service valves for the hot & cold taps (might as well, in case the cold one goes next);
4. turn the main water back on & check that the service valves don't leak;
5. turn the boiler control for hot water back on (so she can use hot water at the other sinks);
6. fix the dodgy tap as necessary, reconnect, & turn the new service valves on.

[Roger Hayter]

I assume the CH can't work with the hot water control turned off? This seems to be true of all the combi boiler designs I've seen, though I am happy to be proved ignorant.

[newshound]

Certainly my experience. Forget items 1 and 5.

[Adam Funk]

I was wrong about that --- the HW control knob ranges from low to high, not including off.

AFAICT the CH did keep running with the water supply (main stopcock) turned off; but I was wrong about being able to turn the HW function off at the boiler (without turning the boiler completely off).