Low hot water pressure/flow - seeking advice

[Rachel-q3zuw]

Looking for some advice regarding poor hot water flow rates in my house please.

Lived here about 7 years and hot water has always been on the rubbish side. Recently had a 30KW combi boiler replaced with another, rated for 12 /lpm DHW output, was hoping it might improve things but made no difference. Plumber says its just the way the house is and there's not a lot he can do about it.

Hubby has taken some measurements:

Static pressure at outside tap (next to incoming supply): 1.9/2.0 bar typically.
Flow rate outside tap: 16 - 20 /lpm

Kitchen cold tap: 8 /lpm
Kitchen hot tap: 7 /lpm

Bath cold tap: 13 /lpm
Bath hot tap: 8 /lpm

Thermostatic shower @38c: 6 - 7 /lpm.

All internal pipework 15mm.

Hubby's theory is that the flow rates are poor in the kitchen, and with the boiler being located here, it might not be receiving great cold flow to in turn heat up and pump out on the hot water side. Bit weird that the bathroom, which is much further away from the incoming main, receives much better cold flow rate than the kitchen, where the main comes in. Hubby wonders if the pipework in kitchen might be restricting flow, and wonders if replacing the 15mm pipe with 22mm from internal supply stop tap to near the boiler might help?

Any thoughts?

[netherfield]

Some taps might have pressure restriction fitted, causing poor flow rates.

If you're in a hard water area pipes might me furring up.

[Magic919]

The combi will only be as good as the cold water flow, it doesn’t pump anything.

Have a look at running 22mm as that would help. Hopefully it’s that size from the stopcock.

Maybe try to look for a better plumber.

[Rachel-q3zuw]

netherfield said:

Some taps might have pressure restriction fitted, causing poor flow rates.

If you're in a hard water area pipes might me furring up.

Thanks, hubby is going to look at seeing if he can measure unrestricted flow in kitchen somehow.

We aren't in a hard water area.

[Rachel-q3zuw]

Magic919 said:

The combi will only be as good as the cold water flow, it doesn t pump anything.

Have a look at running 22mm as that would help. Hopefully it s that size from the stopcock.

Maybe try to look for a better plumber.

Thanks. Hubby is trying to figure out how to measure flow on the cold feed into boiler. There is a full bore compression fit lever on the feed beneath the boiler and he's thinking of disconnecting this and measuring the flow.

Also, it's Baxi 800 Combi 2 boiler and he's figured out how to read the measured values from the boiler interface. Outgoing DHW flow speed is 6 l/min with kitchen hot tap on full. Only about 4.3 l/min with shower on. Does this seem low given the boiler is rated for 12 l/min DHW output?

He can easily replace the 15mm feed from stopcock with 22mm, just worried about making it worse

As for the plumber, he was recommended to us as he fit a boiler next door and they were very pleased with it. He's otherwise done a good job, just a bit disappointed he shrugged his shoulders when asked about the poor DHW situation. Not his fault, it was rubbish before tbh.

[Magic919]

He might just not be interested in the job.

Flow rate will depend on what temperature you set the DHW to. It could be coming in at 10 or below and it’s rated with a 35 degree rise. It’ll have to restrict the flow beyond that.

Might be worth measuring the CW feed by the boiler.

Hard to imagine a larger feed could make anything worse.

[Snow and Rocks]

Does the boiler sound the same when heating water as it does when you first turn the heating on?

I.e. Is it running at full bore and roaring away or does it sound like it's throttled back as it modulates it's output to the water volume it has available?

30kw should give a pretty decent shower so sounds much more likely to be flow restrictions or limitations in the incoming main.

[Philvrs]

Any history of remodelling in the kitchen? How old is the house?
I would bet a restrictive isolating valve hidden away somewhere when the sink was moved or something.

[Rachel-q3zuw]

Snow and Rocks said:

Does the boiler sound the same when heating water as it does when you first turn the heating on?

I.e. Is it running at full bore and roaring away or does it sound like it's throttled back as it modulates it's output to the water volume it has available?

30kw should give a pretty decent shower so sounds much more likely to be flow restrictions or limitations in the incoming main.

It does, to my untrained ears, sound a bit quieter on DHW than it does for heating. Will have a proper listen in a bit.

Edited by Rachel-q3zuw on Monday 23 March 15:15

[Rachel-q3zuw]

Philvrs said:

Any history of remodelling in the kitchen? How old is the house?
I would bet a restrictive isolating valve hidden away somewhere when the sink was moved or something.

It s a 1936 detached with a kitchen extension. The plumbing is all fairly modern however, done in the 2000 s when the extension was done.

One thing that has changed is the incoming water supply pipe was relocated. To cut a long story short, the old lead supply pipe burst and to avoid digging up what was then a brand new tarmac driveway, a new 25mm MDPE pipe was routed to the other side of house where it was connected to the existing 15mm feed to outside tap. Before, it used to come in in next room on same side of boiler, changed to 15mm copper and ran about 9 metres to boiler. Now it has to cover about 15 metres in 15mm to reach the boiler, hence why my husband wondered about replacing this with 22mm.

Edited by Rachel-q3zuw on Monday 23 March 15:16

[Rachel-q3zuw]

Magic919 said:

He might just not be interested in the job.

Flow rate will depend on what temperature you set the DHW to. It could be coming in at 10 or below and it s rated with a 35 degree rise. It ll have to restrict the flow beyond that.

Might be worth measuring the CW feed by the boiler.

Hard to imagine a larger feed could make anything worse.

Interesting thanks. We had the DHW temp set at 55c, dialled it down to 50c and it's made a small .4 l/m difference to the boiler output. Shower runs slightly better.

[Black_S3]

Rachel-q3zuw said:

Looking for some advice regarding poor hot water flow rates in my house please.

Lived here about 7 years and hot water has always been on the rubbish side. Recently had a 30KW combi boiler replaced with another, rated for 12 /lpm DHW output, was hoping it might improve things but made no difference. Plumber says its just the way the house is and there's not a lot he can do about it.

Hubby has taken some measurements:

Static pressure at outside tap (next to incoming supply): 1.9/2.0 bar typically.
Flow rate outside tap: 16 - 20 /lpm

Kitchen cold tap: 8 /lpm
Kitchen hot tap: 7 /lpm

Bath cold tap: 13 /lpm
Bath hot tap: 8 /lpm

Thermostatic shower @38c: 6 - 7 /lpm.

All internal pipework 15mm.

Hubby's theory is that the flow rates are poor in the kitchen, and with the boiler being located here, it might not be receiving great cold flow to in turn heat up and pump out on the hot water side. Bit weird that the bathroom, which is much further away from the incoming main, receives much better cold flow rate than the kitchen, where the main comes in. Hubby wonders if the pipework in kitchen might be restricting flow, and wonders if replacing the 15mm pipe with 22mm from internal supply stop tap to near the boiler might help?

Any thoughts?

assuming the shower is above the bath taps that are 13lpm cold and 8lpm hot (at approx 60 degrees) when running together you should be able to easily acheive 10lpm @ 38 degrees on the shower. First thing I'd be doing is assuming its a bar shower pull that off the wall and check the inlet filters arent cloged and also check for any flow restrictors in the shower head etc.

As others have said theres probably a flow restrictor on the kitchen tap - usually the very end of the tap unscrews.

15mm is generally ok for around 15lpm at one outlet - aslong as the boiler isnt sharing a 15mm cold feed with the bathroom or kitchen sink it will be find to cope with a combi.

[AndrewT1275]

Rachel-q3zuw said:

.....now it has to cover about 15 metres in 15mm to reach the boiler, hence why my husband wondered about replacing this with 22mm.

Edited by Rachel-q3zuw on Monday 23 March 15:16

At 2 bar pressure over 15 metres the flow will be around 12l/min and that's ignoring any other potential restrictions. If you can easily change that to 22mm then you should try that as it should make a material difference as the basic flow rate would be nearer 40l/min.

This obviously assumes you don't have other restrictions elsewhere but it is the most obvious starting point.

[B'stard Child]

AndrewT1275 said:

Rachel-q3zuw said:

.....now it has to cover about 15 metres in 15mm to reach the boiler, hence why my husband wondered about replacing this with 22mm.

Edited by Rachel-q3zuw on Monday 23 March 15:16

At 2 bar pressure over 15 metres the flow will be around 12l/min and that's ignoring any other potential restrictions.

That seems a little high - would have expected 7.5 l/m (Based on 2 Bar pressure, !5mm Copper so 13mm internal bore and pipework run of 15 metres)

AndrewT1275 said:

If you can easily change that to 22mm then you should try that as it should make a material difference as the basic flow rate would be nearer 40l/min.

This obviously assumes you don't have other restrictions elsewhere but it is the most obvious starting point.

22 mm would have an internal bore of 19mm so same pressure and length of pipework would give 25 l/min so definitely a good increase

Unless my maths is wrong?

[Rachel-q3zuw]

Black_S3 said:

assuming the shower is above the bath taps that are 13lpm cold and 8lpm hot (at approx 60 degrees) when running together you should be able to easily acheive 10lpm @ 38 degrees on the shower. First thing I'd be doing is assuming its a bar shower pull that off the wall and check the inlet filters arent cloged and also check for any flow restrictors in the shower head etc.

As others have said theres probably a flow restrictor on the kitchen tap - usually the very end of the tap unscrews.

15mm is generally ok for around 15lpm at one outlet - aslong as the boiler isnt sharing a 15mm cold feed with the bathroom or kitchen sink it will be find to cope with a combi.

Thanks, more stuff for hubby to check!

With regards flow restrictor on kitchen tap, hubby has just removed and this has resulted in a slight increase to 9 l/m, although he can see flexi hoses beneath the sink, how much these will restrict it further he does not know.

When you say about the boiler not sharing a 15mm cold feed, do you mean as physically plumbed in or running multiple things as once? Because he can see that the 15mm cold feed from the stopcock splits off to the bathroom before it reaches the boiler. It also splits just before the boiler to feed the kitchen taps and utilities. Is this as it should be or poor design?

Hubby is also wondering, if he runs 22mm to the boiler (or very near), will it make much difference bearing in mind the boiler cold feed inlet is 15mm?

Edited by Rachel-q3zuw on Monday 23 March 17:41

[Black_S3]

B'stard Child said:

AndrewT1275 said:

Rachel-q3zuw said:

.....now it has to cover about 15 metres in 15mm to reach the boiler, hence why my husband wondered about replacing this with 22mm.

Edited by Rachel-q3zuw on Monday 23 March 15:16

At 2 bar pressure over 15 metres the flow will be around 12l/min and that's ignoring any other potential restrictions.

That seems a little high - would have expected 7.5 l/m (Based on 2 Bar pressure, !5mm Copper so 13mm internal bore and pipework run of 15 metres)

AndrewT1275 said:

If you can easily change that to 22mm then you should try that as it should make a material difference as the basic flow rate would be nearer 40l/min.

This obviously assumes you don't have other restrictions elsewhere but it is the most obvious starting point.

22 mm would have an internal bore of 19mm so same pressure and length of pipework would give 25 l/min so definitely a good increase

Unless my maths is wrong?

I dont think either of the maths is wrong - 15lpm for 15mm is on the optermistic side but its generally fine to assume 15mm cold feed is OK for a 30kw combi assuming nothing else is teeing off. If anything is teeing off it then yes - 22mm up to that tee every day.

I think where people get tripped up is the boiler will be able to deliver a 30 degree rise at 12LPM. Assuming an incoming main temp at 10 degrees thats only 12lpm at 40 degrees at the outlet if the boiler... Realistically the boiler HW temp will be set to 50+ so youre likely looking at more like 10lpm that the boiler can deliver to the outlets at 50 degrees.

I think given the bath taps are potentially delivering 20LPM combined with 8lpm of that potentially at 60 degrees the problem with the shower that needs solving might be more straightforward than repiping the house....

[Rachel-q3zuw]

Black_S3 said:

I dont think either of the maths is wrong - 15lpm for 15mm is on the optermistic side but its generally fine to assume 15mm cold feed is OK for a 30kw combi assuming nothing else is teeing off. If anything is teeing off it then yes - 22mm up to that tee every day.

I think where people get tripped up is the boiler will be able to deliver a 30 degree rise at 12LPM. Assuming an incoming main temp at 10 degrees thats only 12lpm at 40 degrees at the outlet if the boiler... Realistically the boiler HW temp will be set to 50+ so youre likely looking at more like 10lpm that the boiler can deliver to the outlets at 50 degrees.

I think given the bath taps are potentially delivering 20LPM combined with 8lpm of that potentially at 60 degrees the problem with the shower that needs solving might be more straightforward than repiping the house....

The shower was fitted new about a year ago, I'd be surprised if it was clogged up yet, but hubby will check. It is a no-name bar shower, probably el cheapo chinesium. Do you think it might be worth replacing?

[Black_S3]

Rachel-q3zuw said:

The shower was fitted new about a year ago, I'd be surprised if it was clogged up yet, but hubby will check. It is a no-name bar shower, probably el cheapo chinesium. Do you think it might be worth replacing?

Loads of people are overly pasting every compression fitting these days so isnt too unusual to see the inlet filters full of crap on brand new showers... This is assuming youre getting 12lpm cold and 8lpm hot at 60 odd degrees at the bath taps right next to the shower tho...