Radiator heat, but hot water disappears after about 1 minute

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Radiator heat, but hot water disappears after about 1 minute

Post  KitKilgour on Wed Dec 13, 2017 12:17 pm

I have a Boilermate II installed upstairs and after some loud banging noises as it & some investigation I found that the top-up tank was empty and refilled.

British Gas visited and
a) diagnosed a pump failure (which they replaced),
b) turned up the pressure in the system from 2 to c. 3 I think and
c) unblocked the filler-pipe from the top-up tank into main unit - coat hanger I think.
Main tank filled up and full hot water for a few days.

However, I am now in a situation where the central heating works fine, there is water of some warmth in the top-up tank, but that on turning on the hot tap you get a burst of hot water for c. 1min and then it goes lukewarm for a long time if left running. You might be able to wait an hour and then repeat.
You can see that the downstairs boiler is kicking in after the tap has been running for a few minutes.

So similar symptoms to another post in this forum, except I do have central heating rather than no central heating.

I'm at a bit of a loss. One could speculate that the main tank was quite short of water reducing the amount of immersion that the hot water coil has thus reducing the time available to heat water, but if that was the case I would expect the expansion banging noises to return as in the initial problem at the end of summer

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Re: Radiator heat, but hot water disappears after about 1 minute

Post  mike on Wed Dec 13, 2017 5:59 pm

BM II
No hot water.

It will be
Mixer or blending valve
Or coil scaled up inside

Mike
MGC/H2O
Norfolk

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Thanks - turned out to be mixer valve on current experience

Post  KitKilgour on Fri Dec 15, 2017 12:58 am

i.e. I have had hot water for nearly a day.

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Re: Radiator heat, but hot water disappears after about 1 minute

Post  SidDIYer on Sun Dec 17, 2017 10:10 am

KitKilgour wrote:i.e. I have had hot water for nearly a day.

Just wondering, was the CH running when you were having the hot water problems? It is better when the CH is not running?

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[comment] No difference with CH running or not

Post  KitKilgour on Sun Dec 17, 2017 1:57 pm

SID - I did check - 6am bath still ran cold, even before the CH was on. It does seem to be fixed now (fingers crossed)

SidDIYer wrote:
KitKilgour wrote:i.e. I have had hot water for nearly a day.

Just wondering, was the CH running when you were having the hot water problems?  It is better when the CH is not running?

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Re: Radiator heat, but hot water disappears after about 1 minute

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