Switch to a combi boiler

[Randers123!]

Hi , hoping someone can advise me , we currently have had our old vented boiler removed from the loft as it was old and are planning on doing a loft extension , so wanted to move downstairs to the airing cupboard in 1 of the bedrooms where the old hot water tank was , I had 3 plumbers come round and my main concern was that I wanted a decent shower as we had a pumped aqualisa.
All plumbers said combis are brilliant these days you should be fine and have a decent shower anyway so we went ahead and had a Glowworm Ultimate 35 fitted . Anyway the heating is great but the shower is terrible , my current specs are 2.5bar of pressure and around 14l /min measured with a bucket , but the shower merely delivers 10l which in my eyes is terrible it’s even worse if one of the kids comes in and brushes there teeth in the morning . Like all family’s do .
After reading some suggestions I fitted a salamander home boost pump to help supply the boiler although this is better the flow rate is still very poor from the shower .
My questions are , is that just a combi for you ? Should I have had a non vented system fitted ?
Could I fit an accumulator to help with the shower ?
Also is it acceptable that 14l /min going in and only 10l/min coming out ?
I spoke to Glowworm and they told me all there boilers whatever the spec are limited to 12l intake , so I removed the limiter to see if it improved which wasn’t that noticeable.
I’m hoping someone else can enlighten me before I rip out the new system and kiss good bye to 3k.
My house is fed with 15mm copper pipe but has ok flow rate .
I’ve checked all filters going in and removed limiter , I’m contemplating buying an accumulator tank to help feed the boiler but is it worth wasting my money or shall I just put that towards a different set up?
Please someone give me an honest answer and no sales crap.
Thanks in advance
Rob

 

[oldbutnotdead]

First thing- your post is in the wrong forum, really needs to be in Plumbing and Heating.
Second, has anyone checked dynamic supply pressure (ie with cold tap wide open, what pressure is pushing water out).
Third, there's not a lot of point fitting boost pumps to the input of a combi.
Fourth (if you have the space) if your dynamic pressure is (as I suspect, pants) look at adding an open vent cylinder & header tank for the bathroom hot water supply

 

[Randers123!]

Thanks for the reply . Oh sorry first time in posting can I move the post.
When you say supply pressure ? Is that when you use the mug style thing , that was at about 12 goes up slightly with pump on .
I haven’t got much space but was considering fitting a big accumulator tank next to the boiler to supply the cold water feed for boiler and the feed for shower , having a pump fitted does mate somewhat of difference apart from drives us made going on and off all the time

 

[Deleted member 267285]

Glow worm technical are correct, as 14 litres per minute would be limited coming out. What do you have at the taps?

 

[Randers123!]

Hi I have a but 14l going in a 10l coming out of the taps , I understand there will be a drop off but that seems excessive

 

[old duffer]

Hi I have a but 14l going in a 10l coming out of the taps , I understand there will be a drop off but that seems excessive

flow rates are limited by pipe diam and the number of draw points. Also a combi has a "theoretical" output as its based upon temperature rise but will always have an "actual flow" rate at whatever temp it happens to be (restrictions on the internal path through the boiler heat exchanger.
You also need to create "priority flow" of the mains so that the combi always has the maximum available flow rate (the cold water for the house is taken just before the boiler inlet)

 

[Randers123!]

Hi so further to my original post and an update , I have fitted a salamander cold water tank boost , 450l tank with a pump 3.0 bar and capable of 80l/min is brilliant by next question is now regarding flow rates my current glowworm boiler shows 14.2 l , which it doesn’t do even with this beast of a pump , reason I’ve found is there is a restrictior in the inlet for 12l , are all boilers the same it kinda false advertising as this boiler can never produce 14l output when it is limited to 12l via restrictor , just for a test i removed the restrictor which increase flow rates hugely and was fantastic pressure for a shower although the boiler struggles to keep up with heating the water to the desired temp , so have refitted the restrictor ,
My question is are all combis the same even though some show 20l flow rates or is it purely my glowworm budget boiler playing dirty tricks on me. I don’t want to invest in another better quality boiler if I’m gonna come up against the same problem with a restricted inlet.
Any help would be appreciated all I’m after is a decent powerful shower

 

[Madrab]

Certain boilers will have flow limiters in them, that allows the boiler to reach is documented output levels @ 35deg rise regardless of the mains pressure and flow. The HW output is normally governed by the boilers KW rating, the higher the KW then usually the more HW it will deliver in L/Min @ 25deg rise.

Reading between the lines though, are you saying you are pumping the CW flow into the boiler? The boiler should be fed from the mains not the cold cistern in the loft via a pump. I also find it a bit strange that your boiler will state a HW output greater than the flow limiter will allow.

What Glowworm boiler is it and what KW rating?

 

[Randers123!]

Yes basically I was sold a combi after them testing my mains input , and was told my shower would be great ( bear in mind i was coming from a power shower ) so it was my main concern to switching to a combo but was told oh they loads better these days etc etc .
Anyway had it fitted glow worm ultimate3 35c .
My shower was terrible no flow or pressure behind barely getting 10l/min so I contacted them and they said the mains can’t be feeding it enough tried a salamander home boost which helped but got noisey after a few weeks , so I’ve now fitted a tank boost so basically there is no starvation on the cold water feed. The problem is the max flow I can get out of the boiler is 12l/min with the restrictor in which I appreciate has to be there to get the temps up , my question is ? Is there a better combi which actually delivers the numbers it advertises or are they all restricted to 12l/min
Thanks for reply

 

[Johntheo5]

The (my) mains temp is 12.0C just now.
You say the boiler flow is restriced to 12.0LPM?
Combi boiler outputs are more often than not specified at a rise of 35C, (some specify a 40C dT), so your (35kW boiler) specified output might be, 35*860/60/35, 14.3LPM, which should give a DHW temp of, 12+35, 47C.
I would suggest (test) increase the DHW flowtemp setting to 60C, then open a hot tap or taps to give a flowrate of exactly 10.45LPM, then measure the HW temp (if not displayed in the boiler panel) to confirm, this proves that the boiler is giving its rated output, if happy with this then one would think that a 3bar accumulator should/might be able to add 7.46LPM @ 12C to 10.75LPM @ 60C to give a shower flowrate of 17.91LPM @ 40C, (still 35kW), even if not, 12 to 15LPM should be reasonably acceptable?.
Presume the accumulator is boosting the mains supply to the combi as well as elsewhere?.

 

[Elsa TLC]

If your water pressure and flow rates meet the mark then keep the boiler and fit an unvented cylinder

 

[Randers123!]

What alongside the combi , so basically store the hot water along side. The cold water feed side of things is fantastic now. Would the hot water not go cold in the tank or you mean with a immersion heating keeping it hot

 

[Elsa TLC]

What alongside the combi , so basically store the hot water along side. The cold water feed side of things is fantastic now. Would the hot water not go cold in the tank or you mean with a immersion heating keeping it hot

Use your combi like a system boiler.
The primary flow & return would work on an S plan and heat the water in the cylinder vis the coil.

Is the boiler located near any a kitchen or a bathroom?

 

[Randers123!]

No it’s all mounted in the airing cupboard , hence moving to combi as we doing a loft conversion , I’m almost at the point of ripping it all out and putting in a unvented system but someone’s put me off with our standard inlet water supply is merely 11-12/l min with just under 2 bar pressure , they saying it might struggle.

Could you possibly share which style cylinder you are talking about , I’d probably only need 100liters if combi is filling it too

Or even better a diagram of how you think it would plumb ?

Many thanks for your input

 

[Elsa TLC]

It's hard to say without know how your house is designed.

The combi could supply let say a kitchen tap. The unvented cylinder would supply everything else.

Is you have a garage or some other space you could have a break tank and a booster tank