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JamesI, Handyman
Category: Appliance
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Experience:  I have repaired and maintained numerous items over the years, from fridges to freezers, radios to TV's.
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Everhot immersion cylinder. 3 bar until tap turned on then

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Everhot immersion cylinder.
3 bar until tap turned on then pressure drops, why?

I am assuming you have a pressurised system fed directly from mains water if your seeing 3 bar in the tank.

The most likely cause for a pressure drop is insufficient flow rate, into the tank, so you are pulling more water out than you can feed in thus pressure is reducing to compensate.

It may be worth checking all the inlet valves are open \ unrestricted, or put a service valve on taps to reduce the flow rate.

Please let me know if you need anything clarified.

Customer: replied 1 year ago.
That makes sense.
The inlet tap is certainly open and there is then what I think is a one way valve, could these be restricted?
It seems odd that when the basin tap is opened, the water comes out in a flurry but almost immediately reduces to a little more than a dribble.
Is it just the mains water that provides the pressure? Could the tank need bleeding or pressurising?!
Thanks, David
Customer: replied 1 year ago.
I could open all the hot taps (kitchen, bathroom and shower) and see if the flow to each is then 1/3rd as much as if just one tap is open.

The psychics behind water pressure is a little more complicated, opening 3 more taps wouldn't reduce the pressure by a 3rd, as you will probably find there is sufficient volume of water to maintain 2 bar for example with 3 taps open just not 3 bar with one tap open, you also have the benefit of gravity water on the ground floor (assuming the hot water tank is upstairs) will also be playing its part.

What you will find (as is more common on toilets) is the water is switched off over the next second or two the pressure builds ups behind the valve, so when you then turn on the valve its under pressure and you often get pipes which shudder due to sudden pressure differential.

A non return shouldnt cause significant flow rate issues but it has been known, my suggestion would be leave a tap on and measure the mains water pressure and see how many bar its at.

Customer: replied 1 year ago.
The problem is at my ageing parent's apartment, 3miles away, so I can't immediately try things.
The property is on one floor and the tank is on the same floor so no gravity feed.
Should I measure mains pressure by timing the filling of a bucket 'cos if so, how big a bucket and how long should it take please?

You can pick up a pressure gauge like the one here from somewhere like screw fix, and it just screws on the outside tap.

In terms of measuring without a gauge, you could measure flow rate but not pressure, but they are related. I would use a 2L coke bottle, that way your not taking 5 minutes to wait for a bucket to fill, and its a simple measurement unit (2L) if it takes 30 second to fill then the flow rate is 4L per minute.

The simplest way to stabilise pressure is place a pressure reducer on the mains inlet into the tank to drop the pressure to 2.5 bar which would make it less noticeable. Another options is to use smaller pipes \ install restrictive valves on the pipes feeding the taps, this will reduce the flow rate which in turn will maintain the pressure. In addition you could increase the diameter of the inlet \ feeder pipe into the tank, a 22mm pipe is the equivalent to two 15mm pipes, due to surface friction.

If this is causing significant issues, and your seeing the water flow rate drop to next to nothing this would suggest a blockage of some description, as this wouldnt impact pressure just flow rate.

Customer: replied 1 year ago.
I'll try the 2L bottle tomorrow and let you know.
It sounds like it's the flow to the tank.
Nothing has changed since everything was fine, except the electricity was turned off and nothing used for 2 weeks. Only since then has this problem arisen.

Could there be a water pump which has tripped?

Customer: replied 1 year ago.
How do I find out?
Where would the pump be?

If the pump is to increase water pressure across the entire house it would be where the hot and cold water feed are, so probably directly after the hot water tank, probably spurred off the immersion circuit.

Customer: replied 1 year ago.
I'll go and have a look this morning but I don't think there is a pump.
I'll measure the flow from hot and cold individually, in both room.
Thanks, David
Customer: replied 1 year ago.
Hi James,
I've measured the flow as follows:-
Bathroom basin - Hot 2L/min
- Cold 2Ll/min
Kitchen sink - Hot 4L/min
- Cold 12L/min
I can't see a pump or wiring and it is only a 2 bed apartment on one floor.
I think you're right with a blockage.
I can send you photos if you know how I get them off my iphone please? There appear to be 2 non return valves and a stop valve after the incoming stopcock and the pressure gauge which reads 3 bar (until you turn a tap on then it drops below 1).
There is also a regulator in the line marked 'PRERECLAGE POUR UTILISATION 3 BARS'.
Thanks, David

Hi David,

Photos probably wont help, but you can upload them here and share the link,

I am conscious this has turned into multiple questions, and I am limited to how much time I can spend on going back and forth with one question.

Clearly the sink is coming from the rising main and hence has a higher flow rate, the regulator you have is designed to reduce the pressure down, and the writing just says it needs to be calibrated before its used, the purpose of the valve is to stop the pressure building up in the cylinder.

The Bathroom basins are probably running off 15mm pipes so this may be one reason for the restricted flow, but to address the issue you need to get a plumber in who can intercept the pipes and different locates to measure flow rate and water pressure, and then see if there is a valve causing the problem.

My money is still on a valve which isnt fully open.

Customer: replied 1 year ago.
How about if I shut off the mains, drain the tank if necessary and take out the one way valves and clean or replace them?

If your going to the effort of removing the valves I would replace them, at least you can then work back towards the taps once you have checked\replaced those valves.


Customer: replied 1 year ago.
Hi James,
I'll get 2 non return valves then and have a go.
Hopefully full flow will then return.
Thanks, David

My colleague also advised the model of pressure regulator you have (with the french writing) should have a strainer inside it, and this often becomes blocked, so would be worth shutting off the water at the stop cock and then removing that and giving it a good clean.

Appreciate if you can rate the service received to date.



Customer: replied 1 year ago.
Thanks James, I'm away now for 2 days and will check the valves and filter when I get back, David

Hi Daivd,

Appreciate if you could rate the service received.



Customer: replied 1 year ago.
Hi James, your assessment and advice has been clear, appropriate and helpful. The problem remains but I know what to do next and am optimistic that this will be the cure. I'll let you know, David

There should be a star rating somewhere on the message which is used for Just Answer to then pay me for my time.

Appreciate your help, enjoy your time away.

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