New combi fitted, hot water flow...

23 Aug 2004
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United Kingdom
Just had a new Ariston Combi A HE Condensing unit fitted which is nice enough but not for the upstairs taps. The boiler is fitted in the kitchen and the hot tap in the kitchen works perfectly at basically mains pressure, up stairs in the bathroom (directly above the kitchen) tho it drops off to a trickle despite the down stairs mains pressure. The cold taps in the bathroom still have high pressure(ish) tho, certainly there is a reduction compared with the kitchen sink but not like the drop off of the hot water feed.

Could the problem be that from the boiler the hot feed to the bathroom is a 15mm pipe run, would swapping this over to 22mm make a difference?

One other question re: Combi's, having never personally had one before is it normal when someone opens up a cold water tape else where the hot taps basically turn from there normal trickle to a slow drip?

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You have not mentioned what power boiler you have but presumably the cheaper 24 kW.

This will in effect only supply one hot tap at a time.

Using cold water taps will affect the hot water flow if your mains supply is of limited flow.

Your CORGI registered installer should have explained all of these things to you!

Sorry i should have mentioned, it's a 30 kw unit. They did explain it several things but i'm guilty of after having a the gas and hot water off all day of just wanting the thing "working" so i could do the washing up, washing, bath etc. i just wanted them to pack up and leave us to it.

The mains supply tho is not of limited flow tho, it's like a pressure washer flow rate in the kitchen for both hot and cold taps (and the hot is very hot as per boiler setting).
You should ask the installer of your combi to look into these problems since they are all related to the installation. The installer must commission the boiler and unsure that the hot water supply is as it should be to all taps.
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So: the cold mains pressure is good, kitchen hot tap pressure and flow are good, and the bathroom hot tap P & F are poor even when that's the only tap on in the house.

If it's just one bathroom tap then it's just that tap which is faulty/blocked, but if more taps are affected (and affect each other badly) then it sounds like the pipe is blocked. 15mm should be fine for all the combi can put out.
Thanks for all the replies, i've found the problem out, it's me.

After what you put ChrisR i decided to try out each tap and see what the actual flows were like. I took a 2l jug and filled it using kitchen, sink, bath taps (h & c)

Kitchen - C - 7.x sec
Kitchen - H - 13.x sec
Bath & sink gave same speeds - H - 14.x / C - 8.x sec

All close enough to each other, about 8l / min at full DHW temp of 60c, the spec say it's good for 12.9l / min @ 35c (which i'll take with a pinch of salt). The kitchen taps appeared to be equal pressure (h & c) due to the spray from them but as i found out it wasn't the case. What didn't help either was last night as i was running a bath missus had put the washing machine on and decided to do the pots as well which was unknown to me when i posted.

Cheers again for the replies, next time i'll double check what the other half has been up to before i post :cool: This combi lark is going to take some getting used to...

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