COLD MIXER TAP TRIGGERING BOILER

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I've just had a new mixer tap fitted on kitchen sink and now our combi boiler is being triggered even when the tap is set to draw cold water. This should only happen when the tap is drawing from hot. It doesn't happen when the tap is only turned half on, only when it's on full.

This never happened before we changed the tap but previous tap wasn't a mixer. Could the tap have been fitted wrong (by professional plumber) or could it be just a small adjustment is required somewhere?
 
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Hi

Is ther a one way valve (Check valve) on the hot water pipe supplying the mixer tap?

If not the cold water is push back up the hot water pipe back to the hot water tank triggering the boiler to kick in.
 
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Ed_de_Ball said:
If not the cold water is push back up the hot water pipe back to the hot water tank triggering the boiler to kick in.
Can you think of a reason for there being a hot water tank when the OP has said that the hot water is coming from a combi?
 
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Fit a small shock arrestor on the cold mains just after the stopcock.
 
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What's the combi?
Either there's ome air in the pipes, or the new tap is letting water cross over as Ed is suggesting.
Open ALL your taps, one at a time, especially ones you haen't used, FULL, to try to get air out.

But I'm thinking that if you have to open the tap fully, it's a fault with the tap rather than air.
You might end up putting non-return valves in its supply pipes.
 
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Couple of questions.

Is the installation in a bungalow?

Does the DHW pipework rise from the combi then drop down to the draw off points (taps)?

Does the "triggering" only happen if the taps are turned off quickly?

Suggested remidial action/actions.

If gentle operation of the taps ( particularly when turning off) has the effect of not "triggering the combi, and/or part of the DHW pipe work is in the roof space, then the cause is probably air in the pipe work which will not be removed by running the hot taps unless you leave them running long enough to drain your local reservoir.
Just be patient and after a few weeks the problem will most likely have gone away.

However, please keep us informed as to the out come because that will help others who read this forum.

Tim
 
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I've just had a new mixer tap fitted on kitchen sink and now our combi boiler is being triggered even when the tap is set to draw cold water. This should only happen when the tap is drawing from hot. It doesn't happen when the tap is only turned half on, only when it's on full.
I think this indicates that in the cold fully on position the mixer tap is actually drawing some hot too, just enough to trigger the combi but not enough to make the cold water feel noticeably warmer. It may be that a more careful positioning of the tap lever might avoid this.

Of course it's also possibly that the OP is not telling it like it is and that we actually have the combi being briefly triggered by a pressure surge on closing the tap quickly, which is quite common. Other suggestions like cold passing to the hot side of the mixer tap (why? both are at mains pressure) or air pockets in supply pipe (which are easily cleared by mains pressure) don't make sense in relation to what the OP says.
 
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Would be interesting to know what combi it is. If it happened to be an Isar then the slowest of drips or similar, will call for DHW, which would tie in with your reply Chris.
 
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Thanks for all the responses.

It's not a bungalow, the combi's a Worcester 24i and the pipework runs down from the boiler along just above the floor and then up to the taps about 6 feet away.

I've now tried turning the tap off very slowly and it doesn't appear to trigger the combi when I do that, even if I've had the cold on full. I also tried keeping the tap running on cold and low, after triggering the combi to see if it might be drawing some hot, but it stayed icy cold which would suggest it's not drawing any hot.

Would any air in the radiators have an impact?
 
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I'm experiencing this peculiarity after having our old boiler replaced by a condensing one. The old one didn't do it, neither did the one before that, when we lived on the 1st floor (we're currently on the ground floor).

The 2 nearest cold water taps to the boiler (kitchen and outdoor garden) both trigger off the boiler pump even if they're turned on for a fraction of a second. The pump runs for 10-30 secs each time, which is an excessive and un-necessary use of the pump.

The two installers (contractor & sub-contractor) tell me that the boiler is super sensitive, and reacting to the slightest change of water pressure - i.e eveything is working as it should. They seemed to act as if I was the only person to query it.

But the manufacture's own service engineer immediately identified the condition, stating it is caused by a back surge in water pressure. I.e. the boiler is fine, but the plumbing is at fault.

I'm now in a dilemma whether to go back to the installers, employ a separate plumber, or hoping that I'd find the answer by Googling it - and here I am! :confused:
 

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