Question re poor flow rate, measuring flow at stopcock

[EJW]

Hello, I'm a layperson not in the trade. I hope I'm posting this question to the right place. Thanks for your attention.

We are investigating getting a new 32mm mains supply put in by Thames water and re-plumbing internally with 22mm to resolve a poor flow rate in our 1960s house. This will allow us to have a combi and remove hot and cold storage tanks. Flow rate at kitchen tap and cold water storage tank valve is less than 10 litre/min, not enough for a good shower with a combi we are told. Thames Water measure flow rate at external stop valve and it was better than 30 litre/min. The house is plumbed with 15mm pipe throughout. Presure is 2.5 bar in the house and at the external tap.


The new supply and replumbing work will be very disruptive and expensive, so we're not sure if it's all worth it, but the appeal is that it would be a long term 'upgrade' and future proof the house in case we want to put in an extra bathroom and extend a room in the attic later.


The problem is we still don't know why the flow rate is poor in the house, and it could be all this work is not necessary. Is it the 15mm pipework overall, or is there a specific point where it's restricted? I estimate the total distance from external stop to the cold water tank on 2nd floor is 8-10 metres.


Before we embark on booking all the work, it seems sensible to check the flow rate at our internal stop valve first. In fact this was advised by the engineer from Thames Water who visited - he said it was straightforward and I could do it myself. I called a couple of plumbers that we've used in the past and they turned the job down as too small so I'm game to try it myself. I'm ok with practical things generally but have never touched pipework. Please see the attached photo of the stop valve, this is in a box in the corner of the downstairs toilet low down, it's quite awkward to get in there. I'm assuming I just need to turn off supply outside the house and then loosen the collar at the bottom and push the tap vertically to disengage - I can then slip some garden hose over the top of the end of the naked pipe pointing up, run the hose outside, turn on the outside supply again and then measure the flow by filling a bucket with a stopwatch. Does anyone out there have any advice? Do I need a special tool to loosen the collar? My main worry is that I I'll have trouble reconnecting the stopcock and then we have no water - disaster!


My final question is this: what's that valve directly above the stopcock for (2nd photo)? Could that be the source of our poor flow? Plumbers who looked at this haven't commented on it but I didn't specifically ask them. Thanks!

 

[Best]

Hello and welcome. You could possibly check the pressure and flow rate from beyond that stopcock. An outside tap for example would do, but taps are restrictive - especially if modern types. If your mains was turned off at stopcock and your outside tap was easily screwed out from its female fitting, you could have a hose connected directly.
I often just use a bucket with stopwatch method at a outside tap, but only as a rough check

 

[Best]

You have to be aware that there could be restrictive isolating valves, narrow bore flexi hoses and restrictive flow taps really designed for high pressures in your house at minute.
If you do achieve the flow and pressure you want, then also consider an unvented cylinder with a system boiler as a great option.

 

[EJW]

Thanks for the tips, unfortunately we don't have an outside tap. As far as we can tell the pipe going up from the stopcock rises directly to the attic where the cold water tank is. At some point it must also tee off to the kitchen but it's hard to tell where that happens.

 

[EJW]

yes, thanks. the problem is understanding where or what it is that's causing the poor flow and resolving that. At the moment we only have the 'nuclear' option of replacing all the pipework between external supply and where the new boiler would be - very expensive and disruptive.

We may go for a system boiler and vented tank now, and then upgrade to unvented at a later date if we can resolve the flow problem. I presume any modern system boiler is compatible with unvented hot water tanks?

 

[Best]

You can fit a combi boiler and later connect it to an unvented cylinder if you wished. The combi could still supply hot water to nearby taps to the boiler. That's if you achieve the flow & pressure to suit

 

[Chalked]

If you get a good local gas safe heating guy to give you a price for the boiler. He will measure the flow rate and pressure needed for the combi to work.
From what you are saying, the existing main sounds adequate.