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Discuss Hot water coming on combi sometimes other times not in the UK Plumbing Forum | Plumbing Advice area at

Hi guys thankfully not been needing to com on for a while but could do with a pointer.

2 weeks ago I noticed boiler didn’t fire for hot water in kitchen which is next to boiler and cold main in, it came on after a few seconds longer than norm I thought just a blip, but this weekend and since it’s been bad I’m 4 in a block terrace, second from main inlet my mums next door, noticed Sunday as always has happened flow reducing but still strong a good 800ml in 6 seconds but wouldn’t fire up she had her washing machine n tap on put tap off hot water went, she has lower flow than me and same boiler Ariston class HE 30 and gets hot water no bother as did I till Sunday, Scottish water came out just under 2bar into house, with no other taps on, if I run my tap with no others on it’s over a ltr in 6 seconds

Anyway now most days my bathroom sink won’t fire up again a ltr 6 seconds but if I turn on the bath tap it fires up n then open the sink tap close the bath tap n all good. If I flush the loo even the downstairs sink hot won’t come on, yet if the hot waters running on I can turn all taps on to hot or the rest to cold n one hot and boiler maintains hot water.

My mates a plumber/heating engineer not been over yet but suggested it might be the water flow sensors playing up n maybe restricting a bit more flow/blocked. The flow I don’t thinks changed any time n honestly my mums on 400/500 ml per 6 seconds n works ok even with other taps on. The Scottish water guy suggested even flushing the loo shouldn’t stop the kitchen hot coming on as it’s the first demand from the cold main n even said the flow rates fine.

Heating working fine!

Attachments the kitchen sink flow at hot when running bath cold n won’t fire, the others are bathroom sink won’t fire that’s with no other water on n the bath one running hot at that flow rate, any help or advise would be great. My mates going to get the new flow switch anyway but I guess I’m asking could it be that, that is causing the issue like I say it happened couple weeks ago but hot water at bath sink was fine as shaved plenty times now hardly comes on hot.


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