System losing flow/pressure

[PipingMike]

Hello everyone,

I have a problem that has stumped two plumbers so I thought i'd come to a forum to see if anyone out there has had a similar problem.
I live in a top floor flat with its own water supply. The tap in the kitchen has 12litres per minute flow (near where the water enters the flat). The taps in the bathroom and the shower have about 2litres per second. I believe there used to be a system boiler with tank up in the attic. So the water would come in via the kitchen. supply the kitchen tap with adequate flow, then go up to the attic (one floor up) where it would enter the boiler, and return down to the cold taps in the bathroom. At some point it is losing flow but there aren't any leaks anywhere. One plumber suggested its the fact that the house is old and has 22mm pipes rather than 15mm. Its turns back to 15mm pipes as it enters the boiler. I understand that it would slow down in to the 22mm pipes but surely it should speed up when it goes back to 15mm (assuming a closed loop). The lack of flow into the boiler means the hot water is intermittent.

Does anyone have any ideas?

many thanks,

Mike

 

[Deleted member 120897]

This doesn’t make sense, you’re saying it’s losing pressure/flow but getting 120 litres per minute in the bathroom?

 

[Chuck]

Am I correct to assume you meant '2 litre per minute' not 'per second'?

When your plumber said this "the fact that the house is old and has 22mm pipes rather than 15mm" they were probably explaining why they thought your house has an indirect (low pressure) cold supply to the boiler and bathroom.

You need to find out what is actually in the roof now. If you can't get access easily, can you hear a tank filling after you have run a bath? A plumber will be able to tell by comparing the static pressures measured at the kitchen and bathroom taps.

Plumbing in old blocks of flats is tricky to get right. Needs a plumber with the right knowledge/experience, the cooperation of the freeholder and possibly coordination with other flats.

 

[PipingMike]

Am I correct to assume you meant '2 litre per minute' not 'per second'?

When your plumber said this "the fact that the house is old and has 22mm pipes rather than 15mm" they were probably explaining why they thought your house has an indirect (low pressure) cold supply to the boiler and bathroom.

You need to find out what is actually in the roof now. If you can't get access easily, can you hear a tank filling after you have run a bath? A plumber will be able to tell by comparing the static pressures measured at the kitchen and bathroom taps.

Plumbing in old blocks of flats is tricky to get right. Needs a plumber with the right knowledge/experience, the cooperation of the freeholder and possibly coordination with other flats.

I did mean per minute.

I can get in to the attic. There is just a combi boiler there. The problem is that there is inadequate flow to that boiler. It is difficult to work out where or why the flow is decreasing. Do you think installing a pump just before the boiler will help the problem?

Many thanks,

Mike

 

[Chuck]

Do you think installing a pump just before the boiler will help the problem?

I wouldn't want to comment based on the information given. I'd want to understand the root cause of a problem before trying anything like that; guesswork can be very expensive.

When you say 'taps' do you mean hot, cold or both? Have you searched for stopcocks/isolator valves in the flow path and checked that they are properly open?

Measurements of static and dynamic pressure at the inlet and outlet of the boiler would clarify what the issue is.

 

[PipingMike]

So the cold tap in the kitchen is fine.
The hot and cold in the bathroom is weak. The shower is weak also.
The hot taps start with higher pressure and drop off in a few seconds.
I have searched for stopccks/isolator valves and there are none in the visible areas.

If the pressure measurement in to the boiler shows it's insufficient then would a pump sort the problem? Or would the cast there is probably a stopcock/isolator valve prevent the pump from working?

many thanks,
Mike

 

[Dave Moore]

I did mean per minute.

I can get in to the attic. There is just a combi boiler there. The problem is that there is inadequate flow to that boiler. It is difficult to work out where or why the flow is decreasing. Do you think installing a pump just before the boiler will help the problem?

Many thanks,

Mike

are there any isolation valves before the boiler that might be either not opening correctly so reducing the orifice and therefore the flow?

 

[Timmy D]

You need to test the flow rate going into the boiler.

Turn off water, disconnect boiler cold inlet and run it into a bucket and measure/time lpm.

It’s possible that when the tank was being drained, debris enter the pipework and has blocked the aerators.

Have you removed and cleaned the aerator/s. If not, clean the basin and report back.