Poor flow of hot water in bath

[Cylonmaster]

The hot & cold pipes to my bath are 15mm, shouldn't they be 21mm. The hot water is feed from a hot water tank and is a dribble whilst the cold is very strong. Should I have the pipes changed to 21mm or would an electric pump on the hot water feed suffice? If fitting a pump, are they robust and how long should they last before being renewed?
As a plumber finding this in your house, what would you do?

 

[ShaunCorbs]

Is the tank feeding the hot water in the loft or ontop of the cylinder?

 

[Deleted member 120897]

Are you referring to a vented cylinder or unvented? If vented then absolutely, the pipes should be larger bore, as it’s typically low pressure. If you have an unvented hot water cylinder then 15mm should be ok as it should be equal to your incoming main or pressure reduced if quite high.

 

[Cylonmaster]

Hi, the hot water comes from the top of the hot water cylinder. The cylinder was with the house when bought 15 years ago so I expect it'll be vented. Would a pump suffice or is it a strip out and re-plumb?

 

[Cylonmaster]

Or would fitting a non vented cylinder solve the problem?

 

[Deleted member 120897]

There seems to be some guesswork here. Are you able to upload some photos of cylinder?

 

[Cylonmaster]

The pictures show the tank and the pipework to the bath. This was put in by a plumber who said it's the taps that are causing the problem. The feeder pipes rising from the floor aren't the original pipes

 

[ShaunCorbs]

Would get rid of them valves attached to the pipework that comes out the floor your flow should be a lot better with them removed

 

[Deleted member 120897]

Thanks for photos. You have a vented cylinder, above this somewhere will be a cold water storage cistern, which the higher up it is, the better the pressure and equally flow rate. Hard to tell, but there appears to be a gate valve or 2 on the hot water from the top of the cylinder, which if not fully open, will restrict the flow. I would also be inclined to replace the hot pipe for 22mm for decent flow rate, and I would also have it separated from touching the cold pipe to prevent undue warming (water regulations).

 

[Cylonmaster]

So is an electric pump not a good option on the hot water supply? Changing the pipe will probably require the bath out and flooring lifted etc.

 

[Ben-gee]

You say you’ve been there for 15 years, is this a new problem?
Have you recently had work done on the system?
By the way that work under the bath has not been done by a plumber, at least not a good one.

What is that flexible pipe going through the wall with duct tape on it ? (Hopefully from a fan downstairs?)

 

[Cylonmaster]

The bathroom was re-fitted 5 years ago. It was a qualified plumber that I used. His response to the poor flow was, wrong taps, needed a pressurised water tank. Neither of which seemed correct. Sadly we've lived with it since and have only now decided to look for a resolution. Yes it's a fan from the downstairs shower room.

 

[Deleted member 120897]

Who bought the taps and who fitted them?

 

[snowhead]

As Shaun, the service valves don't look to be full bore, so will be a restriction.
Also the 15mm plastic pipe is not 15mm internally, so will be another restriction and flexis' are even worse if there are any at the taps.

I'm surprised it's 15mm hot out the floor and not 22mm if it's always been vented.

Also as Undertrained, what do the taps look like, they may be High pressure (unvented) only.?

 

[Cylonmaster]

All the gear, shower, bath and fitting bought from the same supplier and fitted by the same plumber, I don't see how the taps could be at fault, they're bath taps with an extension shower fitment.

 

[Ben-gee]

The bath taps are probably high pressure ones- you can get ones designed specifically to work on low pressure. The supplier and or plumber should have asked what system you had and then this would have been sorted before purchase.

However I’m with snowhead , surprised a gravity system has 15 mm pipes for bath . It makes me think he has used the basin feeds for the bath - was there a redesign of the bathroom with things moved around?

Unfortunately for you it looks as though you have had poor service from plumber and bathroom shop.

 

[Basher]

I don't see how the taps could be at fault, they're bath taps with an extension shower fitment.

Like others here, I was suspicious that the bath taps might be a high-pressure design for unvented, but I've found what I believe to be the same Hudson Reed tap set (the OP's photo shows the 'HR'), and though not the best of makes, the manuf. spec says they are low pressure, suitable for a minimum 0.2 Bar supply, so I think we should stop blaming the plumber for selecting the wrong tap set, whatever else he did wrong! 🤪
Is the Hudson Reed spec just overly optimistic?

Hudson Reed Kubix Square 4 Tap Hole Bath Shower Mixer Tap & Shower Kit - KUB005

DimensionsHeight - 170mmWidth (Front to Back) - 50mmDepth (Top to Bottom) - 163mmSpout Reach - 154mmSpout Height - 163mmProduct FeaturesFinish - ChromeMaterial - BrassMinimum Bar Pressure - 0.2 Bar - Low Pressure Additional InformationInstallation RequiredSwivel spoutHigh quality brass internals...

www.tapsuk.com

 

[Deleted member 120897]

@Basher— we don’t know the minimum pressure available, as we don’t know the location of the cwsc. Also plumber is blaming the taps, which the plumber has installed. There should be an amicable solution for the OP here from the plumber.

 

[Ben-gee]

As pointed out by undertrained earlier, be a good idea to check out the gate valves - they often seize/snap spindle in a not fully open position.

I’d try draining down and replace all gate valves with full bore lever valves and see how it is - makes all future work easier too so nothing lost.

 

[Ric2013]

I'm usually reluctant to recommend pumps as they SEEM like a waste of electricity. But I worked out a comparison once for a customer and the extra wasted heat from the water content in the 'dead leg' of the the 22mm pipe runs compared with 15mm pipe runs and energy used by a pump showed that pumping the water through a smaller pipe saved energy (and that was for a full-size shower pump, not an inline Shower Power Booster which, while not being quite as powerful, uses much less energy and is cheaper to install) If installed correctly, pumps should last quite a few years, though that no longer seems to mean 20-30 as it used to in the old days. The warranty may length may give you some idea of durability, though I have known cheap pumps last for 10 years or more and you may be lucky.

The OP's plumbing looks like an old system that has evolved over the years. These types of systems often have pipe runs that reduce the available head of pressure at the tap along their length due to numerous joints and poor plumbing practice by at least one of the many installers (the plastic pipe will have smaller bore than copper and that doesn't help either!). Or, as has been suggested, partially shut or small-bore valves. The standing head (height of water level in loft cistern above the bath taps (1bar =10m.)) is probably less important than the pipe runs.

In my own house, I have improved the water flow from my existing bath tap from 4 litres/minute to 22 litres/minute just by putting a new 22mm pipe run between the cylinder and the bath. But then I was meticulous about deburring, minimising pipe length, and getting my bends as smooth and streamlined as possible and wasn't concerned about energy use as the bath is not used often and mostly in winter.

The OP's taps (if that link is correct) show a flow rate of 4 litres a minute at 0.1 bar. This will be at the working pressure (i.e. standing head as above MINUS any loss of head along the pipe run). It is quite possible that the available head (working pressure) at the tap is only 0.1 bar on a gravity system. If the OP's taps are running much faster when running cold, the installation may have mains cold and cylinder hot - it's more common than people think.

 

[Ric2013]

The bath taps are probably high pressure ones- you can get ones designed specifically to work on low pressure. The supplier and or plumber should have asked what system you had and then this would have been sorted before purchase.

However I’m with snowhead , surprised a gravity system has 15 mm pipes for bath . It makes me think he has used the basin feeds for the bath - was there a redesign of the bathroom with things moved around?

Unfortunately for you it looks as though you have had poor service from plumber and bathroom shop.

If that's plastic pipe to the bath, it's worse than it would be if it were 15mm copper and the pipe inserts themselves are probably quite a restriction.

Quite honestly, on gravity-pressure installations, I like to see screwdown type rubber washered taps to BS1010 or BS5412. Old-fashioned, I know, but they give a decent flow at working pressures down to 0.1bar. I reckon you're right and that those taps may be designed to work at low pressures, but not to work WELL.