Switch to a combi boiler

[Johntheo5]

I know this might only bre considered as a stop gap measure but........
if you assume a average yearly mains temp of say 8C and a required HW temp of 40C, you could consider installing a restrictor in the shower outlet to give say 10LPM
At 1OLPM the boiler will only be running at ~ 65% output so around 12kW spare thermal capacity to help deal with a hot tap opened elsewhere at ~ 5 to 5.5LPM, this assumes a thermostatic shower and the boiler DHW set to 45C, its a compromise but maybe less painful until you finally decide on your next step.

 

[Madrab]

Ah thanks I don’t doubt the boiler is not working correctly , it’s great if you live on your own and have a good water supply but we are a busy house of 4 , and used to having a gravity fed system with a power shower

OK ... to be frank ... if you want an equivalent shower experience where it isn't impacted by other users in the house, a combi probably isn't going to cut it. Even if you go larger there will always be a noticeable impact to the bathing experience.

I have a client that runs a Greenstar 42CDI - not a bad boiler with one (edit) of the better HW outputs @ 16L/min @ 40deg rise +/-15% so really a 35deg rise and the property has a 3 bar @ 17L/Min Dynamic cold mains. They have a high flow rain shower and the owner is constantly complaining about the drops in flow and temp before the thermo cartridge catches up when say the washing machine kicks in, someone flushes a toilet or the sink gets used.

The long and the short of it is combi's just aren't good boilers when it comes to busy households with reasonable and regular HW requirements where the users do not want to suffer with noticeable drops in performance to those outlets. Don't get me wrong they can be worked with if their use is well managed by household and a lot of households are happy to do that and it works quite effectively. Unfortunately though if you are like me where you don't want to have to think or manage that then there can be too many variables and combi's aren't the most flexible when it comes to supplying multiple HW outlets. The only way a combi is going to cut it is with compromises and usage management as to how and when the HW is used. That doesn't suit everyone.

The only other viable and effective alternative is simply stored HW. I think you need to re-think either the design or what you are happy to accept as far as functionality is concerned. It is unfortunately that it seems you were sold a pretty expensive idea that obviously wasn't going to deliver what you wanted.

 

[Randers123!]

Yes I completely agree I was sold that a combo would be absolutely fine , and if I’m honest it was proper crap like a premier inn shower my wife struggles to get the bubbles out of her hair hence why I added the tank boost system which has helped loads but wasn’t cheap plus it’s really annoying pump runs whenever any water is need in the house. Although the cold water feed now is fantastic.
I just need someone who is not gonna sell me the dream and be reasonable for the right setup , I was thinking of a pressurised system my only hold back is the cold water feed only being 12l/min at 2bar.
Located in Essex so if you know anyone that would be fantastic or could suggest a completely new setup I’m a general builder and happy to plumb anything in just need the boiler signed off.
I’ve had some company quoting me a more powerful combi for £3300 but still being fed bi my tank boost

 

[Elsa TLC]

Yes I completely agree I was sold that a combo would be absolutely fine , and if I’m honest it was proper crap like a premier inn shower my wife struggles to get the bubbles out of her hair hence why I added the tank boost system which has helped loads but wasn’t cheap plus it’s really annoying pump runs whenever any water is need in the house. Although the cold water feed now is fantastic.
I just need someone who is not gonna sell me the dream and be reasonable for the right setup , I was thinking of a pressurised system my only hold back is the cold water feed only being 12l/min at 2bar.
Located in Essex so if you know anyone that would be fantastic or could suggest a completely new setup I’m a general builder and happy to plumb anything in just need the boiler signed off.
I’ve had some company quoting me a more powerful combi for £3300 but still being fed bi my tank boost

What part of Essex?
PM me. If you not far I'll pop in to give you more opinion.

 

[Randers123!]

between Witham and Braintree

 

[Elsa TLC]

between Witham and Braintree

I was coming to Witham yesterday to watch Harlow play, but it never happened.

Im not that way often but if I have a moment I'll pop up and give you the best advice I can.

 

[Randers123!]

That would be great are you a plumber can you do the work or are you just talking advice ?

 

[Elsa TLC]

That would be great are you a plumber can you do the work or are you just talking advice ?

Im a Gas safe registered plumber. I don't like to tie myself up to far away. More local these days.

My carpenter comes from Braintree, it's a nice drive so I wouldn't mind coming up to give you some advice.

 

[Randers123!]

Ok sweet. Keep me posted thanks mate

 

[Johntheo5]

I was thinking of a pressurised system my only hold back is the cold water feed only being 12l/min at 2bar.
I’ve had some company quoting me a more powerful combi for £3300 but still being fed bi my tank boost

If you're considering a UVC for HW supply and a pumped cold then you can still use your pump (& 450l Tank) which will supply 20LPM @ 2.75bar, 25LPM @ 2.6bar and 30LPM @ 2.5 bar. which should be about OK.

I would still take a few tests as suggested in post #46, which should show if its just a thermal capacity problem or a water pressure problem, for whatever reason. If the shower flowrate, set to 10.0LPM, remains unchanged (within reason) when you open a cold tap to give say 5.0LPM then it should have little or no effect on the shower flowrate as the pump pressure will only have fallen by 0.1bar, even if the tap flowrate is 10LPM then the shower should still flow at least 8.0LPM and probably nearer 9.0LPM. If you restrict any HW tap flowrate to 5LPM then the shower temperature should stay quite reasonably OK as the combi's output is still adequate for this (and the hot tap) if set to 45C ish.
If not, then IMO a UVC will not fix any particular issues with the shower control or whatever.

Your combi is definitely fed from the pump and not directly from the mains?.

 

[Randers123!]

Yes everything is fed from the tank boost now , if a cold tap is turned on while in the shower there’s no effect , but if a hot water tap is turned on then I may aswell wash with a flannel , the real problem here is purely the amount of hot water being allowed out of the combi boiler at a steady temperature , like I’ve said I can take out the restrictior in the boiler which improves pressure but than the temperature is unstable as the water is being pushed through the heating element too quickly.
I’m currently looking at the Worcester Highflow 550 combi showing 25l/min output but I’m not too sure is that actually a real figure ? Or just gumf for sale reasons.

 

[Johntheo5]

I wouldn't quite put it that way, you proved yourself that when you opened up all hot taps that the HW temperature fell to a very low level, this was purely because the boiler thermally couldn't supply enough power, (it did run at its rated power output of 35kw) to heat the cold water to say 40C because the flowrate was too high, it really has nothing to do with the water being pushed too quickly through the heating element. For example if the test flowrate was 25LPM then a 35kW will give a dT of, 35*860/60/25, 20.1C, resulting in a HW temp of, 12+20.1, 30.1C, only lukewarm, obviously a 55kW boiler would heat that to, (55*860/60/25)+12, 43.5C.
If the boiler restrictor is still in place, set the DHW temp to 60C, then open one HW tap to give a measured flowrate of (only) 3.0LPM, switch on the shower and adjust the flowrate/temp to say 40C, this should still give you a shower flowrate of 12.8LPM, measure it. If you remove the boiler restrictor and set the DHW temp to 45C, then set the HW tap to give 6.0LPM then the shower flowrate should still be 10.8LPM at 40C, still OK ish.
Obviously it means that you can't open multiple HW taps or say a bath HW tap fully otherwise the HW temperature will fall exactly as it did in your test.

Re your Highflow 550 which I presume is a 55kW combi, this will "only" give a flowrate of 55*860/60/35, 22.5LPM at a dT of 35C, not too far away from its published 25.0LPM which will give a dT of, 55*860/60/25, 31.5C but yes, near enough, happy showering.

 

[Randers123!]

Appreciate your long reply thanks but I’m not looking for a shower at 10l/min , I’ve come from a pukka power shower and have just been dissatisfied ever since a combi was fitted. I’m not saying it doesn’t work properly I just want a pukka shower which takes your skin off whether that be the whole system needs changing again or there’s a work around solution.

 

[Madrab]

What kind of shower do you have? Has that changed?

You mentioned you had a power shower before, was that one fed from a separate pump at the bottom of the HW cylinder feeding a normal shower or did it look like an electric shower, which has an internal pump.

What was the make and model of either the pump and normal shower or the make/model of the power shower itself. That will provide a starting point as to what you had and what's expected.

 

[Johntheo5]

Appreciate your long reply thanks but I’m not looking for a shower at 10l/min , I’ve come from a pukka power shower and have just been dissatisfied ever since a combi was fitted. I’m not saying it doesn’t work properly I just want a pukka shower which takes your skin off whether that be the whole system needs changing again or there’s a work around solution.

IMO, a combi probably best avoided then, while a 55kW will give a flowrate in winter of max 21.3lpm @ 42C from mains at 5C then any other HW (tap) usage will reduce this (showerflow) by whatever the HW tap is flowing at the same time.