Low flow on upstairs taps

[koomber]

Wondering if anyone can help diagnose the fault I'm seeing with my cold water feed upstairs, where we've got very low flow from the cold water taps. The flow from the hot water taps is fine, and is much higher than the cold water.

The cold water is mains fed and is T'd after a pressure reducing valve which feeds the unvented hot water cylinder. The pressure is set to 2.1 bar.

Upstairs there is a shower, toilet and sink all of which are suffering from low flow, particularly the shower, which cuts of the heating due to low flow. I've checked the strainer of the shower and it is not blocked, but the problem is common to all the fittings upstairs.

There is a stopcock on the run up, but I've replaced that with no improvement.

The only things I can think that might be causing the problem is a blockage in the line somewhere or possibly an airlock. Any suggestions? I don't think it's likely to be an issue with the pressure reducing valve as the pressure from the hot water cylinder is fine.

Any suggestions gratefully received!

I've attached a picture showing the lineup after the pressure reducing valve in the hope it helps.

 

[Agile]

That may be a difficult problem to diagnose.

It will not be an airlock. You don't get those on mains derived supplies.

All that I can suggest that you can do is to interrupt the pipe somewhere, probably at this stopcock, and measure the flow rate available there. Expect something like 10-20 li/min.

Tony

 

[koomber]

Cheers Agile, I'll give it a shot. I'll compare the flow at the sink and at the stop cock. I've checked as much of the run as possible up stairs and they are identical, and 22mm most of the way to boot.

Do you think there would be a benefit, whilst having the stop cock opened to flushing the line back down the way? I can easily enough go from the hot tap to the cold and have the end of the pipe onto a hosepipe into a drain/.

 

[ianmcd]

why not give it a try it wont do any harm and might just dislodge something

 

[dilalio]

Yep. Try a backwash, can't hurt but maybe cool the hot water before using that as the medium!
Also, do you have indices/strainers on your cold outlets? Check for that first and see if any debris there. Descale the shower head.

Edit: do you have any blending valves? And, can you isolate your shower(s) in case you are getting crossover at the valves!

 

[koomber]

Dilalio, I was going to post and ask why I should cool the hot water before using it as a medium, but I forgot...

Did the flush. Bodged together some homebrew kit and a few fittings to get it all lashed together. Didn't see anything come out, but the flow out the upstairs tap is about a billion percent better. Did a trial run with the shower and it worked okay once I bled the air down. No annoying cutting the heating on and off. Hopefully it'll work in the morning when the wife comes to use it (In the past after the line has been bled it worked fine immediately after but then pooped itself the next day).

Now, I'll admit I didn't let the hot water cool down before I used it. Which wasn't a big problem since the lines bled down fine. But to get the lash up to fit I had to lift a pipe by about an inch, so when I went to reconnect everything the hot water started coming at me. Fortunately it wasn't too hot and I got the fitting on quick, but still.

Kids, listen to your elders. Don't use hot water to test/flush lines.

 

[dilalio]

when I went to reconnect everything the hot water started coming at me.

You'll only do it once

 

[koomber]

So the problem is not fixed, the shower is still very intermittant, however we can get it to work by running it on high, then reducing it to the medium setting, but is still not ideal.

I bodged a pressure tester (hose pipe + gauge) and hooked it up to the tap upstairs and got about 1.2 bar off it. I also checked the pressure of the hot water tap on a tap on the same level as the tank (since this should in theory show what the pressure is from the PRV as it is approximately on the same level. I only meassured 1.4 bar from the hot tap. Looks like the PRV needs replacing as it should be limited to 2.1 bar, but then it is at least 15 years old and I doubt that it has ever been serviced.

 

[Newboy]

What is the pressure of the incoming main - before the PRV?

 

[koomber]

Pressue was about 4 bar. Pretty decent.

I drained the hot water tank and cleaned out the prv. Lots of corrosion in the body, and the mesh needed a bit of a scrub. Put it back together, along with a gauge attached to check the outgoing pressure. Was reading 2.1 bar. The upstairs taps are reading 1.5-1.6bar and the shower is working after several tests through the day