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boilers / water pressure advice



mothy

Well-known member
Dec 30, 2012
2,094
i'm doing some renovations on my 4 bed 2 bathroom terraced house. storage is limited & flow rate & pressure are poor. I've currently got a combi boiler which if anyone touches any tap or puts on dishwasher / washing machine while someone is in the shower it pretty much stops the shower.

I am about to replace the boiler. Rather than getting another combi i was advised to get a system boiler & unvented cyclinder (which my neighbour says still wont help due to our low pressures). So i have now seen storage combi boilers - i've no idea if these are any good, would help or work.

Do you?

Thanks
 




Lindfield by the Pond

Well-known member
Jan 10, 2009
1,886
Lindfield (near the pond)
Had a combi installed years back, which resulted in about 30 mins to run a bath due to poor pressure. Had the system modified with a pump taking cold from cold tank, through combi, and out nice and hot fairly quickly. Still takes a while to fill the cold tank back up though, but at least we get hot fairly quickly and in sizeable quantity. Couldn't run two baths straight after each other.
 


Raleigh Chopper

New member
Sep 1, 2011
12,054
Plymouth
Far from an expert.Simmo Says is probably your man.
But this is what i have got which may help.
I inherited a combi that was not man enough for the house in the first place, we then had a new bathroom intalled with a very big bath and shower that needed a big push of water (rainfall type thing)
Anyway what they did was to use the combi to fill an unvented cylinder with pump, the combi now only supplies hot water to the kitchen hot tap (the nearest tap) the pressure that the unvented and pump produces is now more than enough for all the hot water we need including the heating.
The pressure on the combi, when it drops, can also be raised by inserting a plastic key and tutning a knob.
 


Rowdey

Well-known member
Jul 7, 2003
2,529
Herne Hill
Far from an expert.Simmo Says is probably your man.
But this is what i have got which may help.
I inherited a combi that was not man enough for the house in the first place, we then had a new bathroom intalled with a very big bath and shower that needed a big push of water (rainfall type thing)
Anyway what they did was to use the combi to fill an unvented cylinder with pump, the combi now only supplies hot water to the kitchen hot tap (the nearest tap) the pressure that the unvented and pump produces is now more than enough for all the hot water we need including the heating.
The pressure on the combi, when it drops, can also be raised by inserting a plastic key and tutning a knob
.

Just to say , these two (hot water pressure, and CH system pressure) are not linked in the way suggested.

You can now, 'pump' your mains water, into a Combi/Unvented Cylinder, which would seem to be your answer. I've fitted the Salamander with good results, but would normally go Stuart Turner when anything 'pump' is required, and they too have a good mains pump.

It's never going to be 'knock out/rain head compatible' but will keep 1.5 bar and 12lp/min (i think..) on the go.
 




BN9 BHA

DOCKERS
NSC Patreon
Jul 14, 2013
21,455
Newhaven
I would get a system boiler installed and a normal hot water cylinder, then buy a Stuart Turner Monsoon pump.
You will have to also have a cold water tank fitted in the loft though.
Much better than the combi you have and your neighbour is correct about the unvented hot water cylinder.
 


Dolph Ins

Well-known member
May 26, 2014
1,525
Mid Sussex
We had same prob. Have fitted an electric shower with its own (very small) cold water tank which only feeds the shower.
 






mothy

Well-known member
Dec 30, 2012
2,094
Thanks for info so far. I'm now looking at a Stuart Turner Flomate mains boost extra low water pressure pump. (Not sure if this can run off a combi or system boiler yet?)

I'm getting 2.5bar pressure & 10litres per min - my water main could def do with upgrading from lead pipe.. & my water feeds from stopcock to boiler are 15mm. Should I look at increasing their size too?

Thanks all
 


Baldseagull

Well-known member
Jan 26, 2012
10,871
Crawley
I have a gravity fed system and storage tank, so lowish pressure upstairs on the hot. I got a couple of small pumps from herehttp://www.showerpowerbooster.co.uk/ that make a decent improvement without it becoming a proper power shower and spiking my water bills.
Had them in about 4 years and well happy with them.
 


BN9 BHA

DOCKERS
NSC Patreon
Jul 14, 2013
21,455
Newhaven
Thanks for info so far. I'm now looking at a Stuart Turner Flomate mains boost extra low water pressure pump. (Not sure if this can run off a combi or system boiler yet?)

I'm getting 2.5bar pressure & 10litres per min - my water main could def do with upgrading from lead pipe.. & my water feeds from stopcock to boiler are 15mm. Should I look at increasing their size too?

Thanks all

Depending what your budget is, it may be worth getting your water main replaced as [MENTION=24827]Justice[/MENTION] has suggested ( post #8 )
Then also get rid of any lead pipe inside your property.
You don't really have to increase the size of the inside water main from the stopcock to the boiler if you are keeping the combi.

If you really wanted an unvented hot water cylinder, it's best to have a 25mm plastic main from the pavement to your house, and then have a 22mm main to the unvented cylinder.

I don't think any of this will help if the whole street has low incoming water pressure.
 




SIMMO SAYS

Well-known member
Jul 31, 2012
11,702
Incommunicado
Far from an expert.Simmo Says is probably your man.
But this is what i have got which may help.
I inherited a combi that was not man enough for the house in the first place, we then had a new bathroom intalled with a very big bath and shower that needed a big push of water (rainfall type thing)
Anyway what they did was to use the combi to fill an unvented cylinder with pump, the combi now only supplies hot water to the kitchen hot tap (the nearest tap) the pressure that the unvented and pump produces is now more than enough for all the hot water we need including the heating.
The pressure on the combi, when it drops, can also be raised by inserting a plastic key and tutning a knob.

Thanks for recommending me.
However I am currently having plumbing problems of my own - bloody boiler :censored:
 


mothy

Well-known member
Dec 30, 2012
2,094
Depending what your budget is, it may be worth getting your water main replaced as [MENTION=24827]Justice[/MENTION] has suggested ( post #8 )
Then also get rid of any lead pipe inside your property.
You don't really have to increase the size of the inside water main from the stopcock to the boiler if you are keeping the combi.

If you really wanted an unvented hot water cylinder, it's best to have a 25mm plastic main from the pavement to your house, and then have a 22mm main to the unvented cylinder.

I don't think any of this will help if the whole street has low incoming water pressure.

My neighbour who is a heating engineer did his from lead to polyurethane pipe a month ago & said the difference was negligable - still - every little helps.

I've spoken to stuart Turner who say 15mm feed from their cold water tank to combi boiler is fine & then my only limitation is the flow rate - their tank pumps out up to 24 litre per min. It only holds 100 litres = it's all over after 8.5 minutes if running 2 showers BUT does mean having a shower isn't interrupted by toilet flushing, tap running, washing machine filling (ever) & on the occasions when 2 showers are going will last & refills in under 10 minutes - also has 12l per min hot water after/ when empty so will never have to wait for a hot tank etc. & can always run 1 shower.. (I think - clearly no expert! )

Thanks all
 


BN9 BHA

DOCKERS
NSC Patreon
Jul 14, 2013
21,455
Newhaven
My neighbour who is a heating engineer did his from lead to polyurethane pipe a month ago & said the difference was negligable - still - every little helps.

I've spoken to stuart Turner who say 15mm feed from their cold water tank to combi boiler is fine & then my only limitation is the flow rate - their tank pumps out up to 24 litre per min. It only holds 100 litres = it's all over after 8.5 minutes if running 2 showers BUT does mean having a shower isn't interrupted by toilet flushing, tap running, washing machine filling (ever) & on the occasions when 2 showers are going will last & refills in under 10 minutes - also has 12l per min hot water after/ when empty so will never have to wait for a hot tank etc. & can always run 1 shower.. (I think - clearly no expert! )

Thanks all

Stuart Turner ' tank ' ? I have only heard of and use their pumps.

As your neighbour is a heating engineer what does he have in his house for hot water?
 




Rowdey

Well-known member
Jul 7, 2003
2,529
Herne Hill
My neighbour who is a heating engineer did his from lead to polyurethane pipe a month ago & said the difference was negligable - still - every little helps.

I've spoken to stuart Turner who say 15mm feed from their cold water tank to combi boiler is fine & then my only limitation is the flow rate - their tank pumps out up to 24 litre per min. It only holds 100 litres = it's all over after 8.5 minutes if running 2 showers BUT does mean having a shower isn't interrupted by toilet flushing, tap running, washing machine filling (ever) & on the occasions when 2 showers are going will last & refills in under 10 minutes - also has 12l per min hot water after/ when empty so will never have to wait for a hot tank etc. & can always run 1 shower.. (I think - clearly no expert! )

Thanks all

Stuart Turner ' tank ' ? I have only heard of and use their pumps.

As your neighbour is a heating engineer what does he have in his house for hot water?

BN9 - They are like a break tank/accumulator with built in pump - Very good piece of kit.

Mothy - you say you'll use the 100l up in 8 mins, does that include the 10l per min you'll be putting back in at the same time ? As you say, it reverts to a constant 12 l/pmin when not on charge anyway.

What combi do you have ? Depending upon KW, it can only make between 10 and 16 litres/pmin hot anyway, so worth ensuring it has a flow restrictor on it. No point in pushing more through it.

Have to say, good pressure, with poor flow, normally sounds like a blockage or your lead pipe is kinked/furred up (or you have a leak in the ground.. worth checking your external stop tap box..)
 


mothy

Well-known member
Dec 30, 2012
2,094
BN9 - They are like a break tank/accumulator with built in pump - Very good piece of kit.

Mothy - you say you'll use the 100l up in 8 mins, does that include the 10l per min you'll be putting back in at the same time ? As you say, it reverts to a constant 12 l/pmin when not on charge anyway.

What combi do you have ? Depending upon KW, it can only make between 10 and 16 litres/pmin hot anyway, so worth ensuring it has a flow restrictor on it. No point in pushing more through it.

Have to say, good pressure, with poor flow, normally sounds like a blockage or your lead pipe is kinked/furred up (or you have a leak in the ground.. worth checking your external stop tap box..)

My 8.5 mins was the difference between running 12l back into it & 24l out of it - that said. Can't seem to find combi with much more than 16l without paying the earth so the 6l difference of 10l refill would last me 16.5 minutes.

My current showers seem to have 8l per min output so would give me a stonking single shower & decent with 2.

My only thoughts are how noisey are these pumps in action & tank when filling up..as tank & pump can only go in kitchen or under stairs cupboard..
 
Last edited:


Rowdey

Well-known member
Jul 7, 2003
2,529
Herne Hill
My 8.5 mins was the difference between running 12l back into it & 24l out of it - that said. Can't seem to find combi with much more than 16l without paying the earth so the 6l difference of 10l refill would last me 16.5 minutes.

My current showers seem to have 8l per min output so would give me a stonking single shower & decent with 2.

My only thoughts are how noisey are these pumps in action & tank when filling up..as tank & pump can only go in kitchen or under stairs cupboard..

Not so bad actually; if you can stretch to a iboost, then it's all built in, and even quieter.
 


mothy

Well-known member
Dec 30, 2012
2,094
Not so bad actually; if you can stretch to a iboost, then it's all built in, and even quieter.

I've just ordered my boiler but still questioning the boost to get.

Do you know if the mains boost refill while discharging? Or do they discharge fully & then refill = can't do same at both times.

& I've looked at iboost. & don't really understand what the difference is / why it's better?

Thanks in advance
 




Rowdey

Well-known member
Jul 7, 2003
2,529
Herne Hill
I've just ordered my boiler but still questioning the boost to get.

Do you know if the mains boost refill while discharging? Or do they discharge fully & then refill = can't do same at both times.

& I've looked at iboost. & don't really understand what the difference is / why it's better?

Thanks in advance

Fill while emptying. Think i-boost is a 'better looking' newer version that you dont need/want to hide away - i'll check after i get kids to bed..!
 


beorhthelm

A. Virgo, Football Genius
Jul 21, 2003
35,265
if i may hijack the plumber's attention for a moment...

my combi boiler has two pipes other than those dealing with cold water in/hot water out. first is copper, goes outside to a foot off the floor and nothing more. second is plastic goes outside and into a nearby waste pipe. what is the name/purpose of these two pipes? the second has become damaged, so need to know what to ask to be replaced, it has small dribble of water come out.
 



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