Leak on hot water loop? - not triggering combi to fire up

30 Apr 2023
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United Kingdom
Hi all

As title, noticed water moving noise when on the loo and nothing was using water.

Turned the stop cock off, it ceased. Started again when stop cock opened.

Have checked all taps and pipes I can physically get to, no leaks.

Went to the boiler (Worcester Greenstar Combi) and on isolating the cold water feed for the hot water, the water noise stopped. Also stopped near the stop cock.

Do I take it that I have a leak on a hot tap somewhere? The flow is not enough to make the boiler fire up, but I checked my water usage and it does seem to have jumped up from £13 a month to £23 (this could be attributed to having a new born however).

I have various pipes in the house under the wooden floor, in concrete floors, in the wall etc so is there any smart way of finding this?

Could it be a leak on the boiler itself? I haven't had the cover off, but there's no water dripping down. I did note the condensate pipe has been spitting out a bit more water but assumed this was down to having the heating on more often and from my simple knowledge, I didn't think the two 'loops' would be linked?

Any ideas greatly appreciated and thanks for you help

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Do you have a water meter? If yes, take a reading, don't use any water for as long as possible (an hour should do, longer makes it easier to get a valid reading)- this with everything in its normal position (IE things not isolated).
Take another reading after that time, turn the main stoptap off, wait another hour or more, take another reading (this just to make sure there's no leak between your house and the street).
Take another reading- this one should be zero. If it isn't .....

Despite the noise stopping when you isolate the boiler supply, my first suspicion would be the toilet flush is passing (modern close-coupled types don't have an overflow). Do check that first- it's easy (isolate feed to cistern or tie the ballvalve up, see if the cistern empties).

After that, the meter readings you took will help with the scale of investigation. You can try and narrow down the leak using a screwdriver or similar as a stethoscope on the pipes where you can get at them.
Does the pressure rise on the boiler without being used?
Hi @oldbutnotdead & @CBW , I do have a meter so will try that. Provided I can get the cover off the damn thing...

Also the boiler pressure isn't moving and hasn't for the last few days when I've checked it.

Thanks to both
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Hi all,

I have done the checks on the meter with all left 'as normal'. Reading was 000046,142 at first. With no water seemingly running, the meter was at 000046,173 an hour later.

With my stopcock turned off, the reading was 000046,516 both times. So no leak on the incomer I don't think.

I've checked all push fits and pipework I can get to and can't see anything.

Will check the loo's now...

EDIT: the loos are fine unfortunately :(
Last edited:
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Reactions: CBW
So 30 litres an hour, 500ml per minute.
That's a decent amount to be losing- equivalent to a very drippy tap (1 drop per second or so).
You'd probably notice that volume coming out of the boiler condensate pipe or prv but it might be worth bagging them anyway (unless you do find the real culprit) before you start lifting floorboards.

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