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Would changing pipe size improve flow rate?

I'm renovating an entire flat. Last year had a Vaillant ecotec pro 24 boiler installed. Bathroom and toilet room have been renovated entirely, and the main bathroom now has a toilet installed.

The plumber was told to run mains cold water to the bathroom (previously only hot water from the boiler, which is connected to mains, ran to the bathroom and toilet room) and he replaced the old copper pipe, which was about 15mm, to a new plastic pipe with a larger diameter (22mm). But, he ran the new pipe from a weird location, there is still about 1metre of old piping in the kitchen.

Now, we have an issue with the bath filler, when turning hot water to max, it would flow very poorly do we told him to replace the hot eater pipe too, because we thought it would improve flow rate. The plumber did it without second guessing, and also ran the new pipe from the same weird location as the new cold water pipe starts. So it kind of looks like this: Boiler > old 15mm pipes > kitchen sink location and split to 22mm pipes.

Now the bath filler tap flow rate seems better, but the water is barely warm, yet when turning the basin tap (right next to bath) on, the water is hot.

Plumber says boiler is too weak and suggests replacing it, or putting some sort of device which would limit the flow rate on that specific bath tap. I have asked him to bring a device to test the flow rate on all taps because I don't believe him.
Why would he waste time and money replacing the piping To thicker diameter if it serves no purpose?
Why would he not run the same diameter piping and not replace the old piping from the starting point?
Would the best solution to make sure the bath filler works, be to limit flow rate on the bath filler?

We are reluctant to discuss this because our contractor gets upset when we criticise their work, but we believe they're wasting resources and not doing the job properly. The new piping is thick and ugly, they will have to use more space along the wall when they cover it up?

Thanks,and apologies if this is a lengthy explanation.

4 Answers from MyBuilder Plumbers

Best Answer

Test the flow of water with a flow cup to each tap,a valliant pro24 will give no more than 9.6 litre ,you can also tell how much water is coming out of the boiler on the d.36 program which will tell you how much water the boiler is delivering


Answered 25th Jan 2012

Unfortunately the vaillant ecotec pro24 is a relatively small boiler 24kW so only produces a low flow rate 9.6 litres per min. This is not sufficient to heat the water through a 22mm pipe, which is why the boiler comes with 15mm hot and cold connections.


Answered 9th Sep 2012

Bath taps with 22mm outlets always look like the flow is poor when used with an average combi ie lower than around 12 ltrs per min .


Answered 26th Jan 2012

Using a weir gauge you can check the flow rate to tell how many litres p/minute is coming into the property at the nearest cold water tap to the stop cock. Then you can check the flow rate frorm the nearest hot water tap to the boiler and then finally to the bath filler. As a rule increasing pipe diameter reduces pressure on combi boilers as it is about volume of water, i.e. the boiler can only heat up water at its optimum flow rate for a certain tempreture (which is normally around 45 degrees), by turning the tempreture up of the hot water, this will in turn decrease the flow of water from the boiler. The bigger the kilowatt of the boiler the greater flow rates of hot water, 24kw = 9-10 L/pm 30kw = 12L/pm and 40kw = 15-17L/pm dependant on boiler manufacturer, you need to check boiler specs for accurate flow rates at 45 degrees rise.


Answered 5th Mar 2012

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