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Water Pressure

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 lone 18 May 2020

Hi

I've been looking at the plumbing in a back room where I have a loo, wash basin, there are pipes running from the wash basin (hot & cold) and they connect to the central heating piping.

The hot tap, it'll loose pressure after 20 seconds or so, is this anything to do with the fact that it draws water from the central heating piping and not from the boiler directly ?

I don't have any water tanks (hot or cold) in the house. I have a Baxi Duo-Tech 24

Thanks 

Jason

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 Andy Johnson 18 May 2020
In reply to lone

> The hot tap, it'll loose pressure after 20 seconds or so, is this anything to do with the fact that it draws water from the central heating piping and not from the boiler directly ?

Are you saying that the tap in plumbed into the radiator circuit?

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 S.Kew 18 May 2020
In reply to lonee

Get a refund if piped to central heating.

I should imagine that you have possibly a faulty tap, or restricted pipework to that tap. If all other hot water taps are ok. If all hot water taps are affected, then it could be a boiler plate heat exchanger problem. I would bet my mortgage that it is piped into domestic supply and not central heating.

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 marsbar 18 May 2020
In reply to lone:

If your taps are connected to the central heating you have bigger issues than the water pressure.   

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In reply to Andy Johnson:

> Are you saying that the tap in plumbed into the radiator circuit?

That would be ... 'unusual'...

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 marsbar 18 May 2020
In reply to captain paranoia:

Especially hot and cold...

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 lone 18 May 2020
In reply to Andy Johnson:

I thought it was on the CH circuit, when I ran the hot tap only one pipe became hot the other pipes Inc the radiator pipes stayed cold. 

The tap still looses pressure though. I think it's not on the radiator circuit as I first thought.

Thanks

Jason

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 Ridge 18 May 2020
In reply to captain paranoia:

> That would be ... 'unusual'...

OP, is your hot water black, has an unusual odour and irritates your skin? If not I don't think it's connected to your central heating system.

Post edited at 22:12
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 webbo 18 May 2020
In reply to lone:

We have a similar problem with our hot water. When we run the shower the radiators get hot. We suspect the diverter valve in the boiler is knackered, which given the thing is about 30 years old is not surprising. We plan to get a new one.

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 marsbar 18 May 2020
In reply to lone:

> I thought it was on the CH circuit, when I ran the hot tap only one pipe became hot the other pipes Inc the radiator pipes stayed cold. 

> The tap still looses pressure though. I think it's not on the radiator circuit as I first thought.

> Thanks

> Jason

If only one pipe gets hot when you turn the hot water on that is good news, the others shouldn't.  

It could be that you need a new tap washer or cartridge.  

Post edited at 22:48
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 lone 18 May 2020
In reply to marsbar:

Thank you. Note to self to turn the water off tomorrow when I get the wrench out.

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 marsbar 18 May 2020
In reply to lone:

I hope that is all it is but I can't promise.  

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 jkarran 19 May 2020
In reply to lone:

There's no way your hot tap draws off the radiator loop, radiator water is black filth. Most likely as the tap valve heats up it expands unevenly and shuts down, our kitchen sink tap does it, it's a right pain in the arse keeping a steady low flow and the boiler lit.

Jk

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 Philip 19 May 2020
In reply to lone:

Does the pressure come back?

If not I think you have a problem with your expansion vessel or maybe a pressure regulator.

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 krikoman 19 May 2020
In reply to lone:

Turn the boiler off, then run the hot tap.

Does it still lose pressure?

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 Mark Edwards 19 May 2020
In reply to lone:

Do other hot taps exhibit the same behaviour or is it just the one in the back room? I’m wondering if there is a restriction somewhere in that line. The pressure builds up while the tap is off giving the good flow until the pressure has reduced back to the restricted flow. Although 20 seconds worth would imply a lot of pipe to hold that much pressure.

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 MattJ753 19 May 2020
In reply to lone:

I'm assuming its a combi boiler? And does it do it at all hot taps in the house? How about the cold taps?

It could be a scaled up plate heat exchanger.

Could be a clogged up filter on the cold water inlet to the boiler, if it has one. 

These would reduce flow, but probably all hot oulets would have the issue. 

If its just that one tap it could be blocked aerator at the tap outlet, or knackered washer/cartridge. Or the washer growing as it gets hot, but this only usually happens when the tap's not very open to start with. 

Wouldn't be pressure vessel related unless you have a mains pressure unvented hot water cylinder, which is a different type of system.

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