5 Bedroom House, 18 Rads, 1xBath, 3xShowers - Combi or System Boiler

[goldfrapp]

Hi

We are currently having an extension built to add a fifth bedroom and a en-suite. We'll end up with 3 showers and a bath and about 18 rads.

The existing 8 year old non-condensing boiler has to be moved and so I am considering replacing the existing 25 year old hot water tank (a weird Gledhill system that constantly heats water).

In an ideal world I know that a new system boiler and a megaflow hot water tank is the way to go but I've been quoted an horrendous amount by British Gas to install it which I can't really afford.

So I am considering replacing the Gledhill with a Worcester Bosch combi in the airing cupboard. We are happy for only one shower to be run at any one time (thats what we have to do now). But will running a hot water tap in the kitchen at the same time affect the running shower ? And what about having the central heating on in the winter and wanting to have a shower. Will a combi cope with 18 rads and a shower.

The alternative is to keep the Gledhill and connect a new system boiler to it such as a Worcester Bosch 40 Cdi.

One other problem to consider is that we have a water softener and the man from BG told me that most boiler manufacturers don't guarantee their boilers if softened water is being supplied to them. Is that true ? Is softened water really bad for boilers ?

What do you think the best way to go is ?

Any advice much appreciated.

 

[Kev the gas]

I recently took out a Gledhill systemmate hot water tank, massive rectangular box 250 ltrs of junk.

I installed a Worcester 42 cdi in its place and the flow rate to the showers has increased!

The Bg guy is correct regarding the softened water, Worcester will not allow softened water in their boiler, can a hard water supply be connected up to the boiler for the central heating side? It is ok for the domestic hot water side.

 

[mfgs]

I wouldn't even entertain a combi with that many showers. No point in having them if you aren't able to use them at the same time, an unvented cylinder is definitely the way to go in my opinion.

 

[Mike Jackson]

I agree, go for an unvented and system boiler. get alternative quotes from a xouple of local guys and the price will be a lot less than the Bg price.

 

[woodytheplumber]

an unvented is best option BY FAR! but if cost is an issue maybe a break tank and a couple of electric showers might be cheeper depending on cable and pipe runs

 

[Kev the gas]

Without starting an argument over what is best unvented /combi.

I have a 300 ltr unvented tank, incoming pressure over 6 bar on a 25mm main, over 25 ltrs flow.
3 bathrooms, all with 8 inch drench showers.
If some one else turns on another shower then the flow is poor, no different to what a combi would produce.

My tank is solar fed hence the size, if I didnt have solar I would not think twice about a high output combi, running costs
must be lower rather than heating a massive tank.

There are 2 adults and 4 kids in the house and we use sh.t loads of water.

Bearing in mind I do more repairs on cheap unvented cylinders than combi boilers in my eyes unvented isnt always better.

 

[Gray0689]

Without starting an argument over what is best unvented /combi.

I have a 300 ltr unvented tank, incoming pressure over 6 bar on a 25mm main, over 25 ltrs flow.
3 bathrooms, all with 8 inch drench showers.
If some one else turns on another shower then the flow is poor, no different to what a combi would produce.

My tank is solar fed hence the size, if I didnt have solar I would not think twice about a high output combi, running costs
must be lower rather than heating a massive tank.

There are 2 adults and 4 kids in the house and we use sh.t loads of water.

Bearing in mind I do more repairs on cheap unvented cylinders than combi boilers in my eyes unvented isnt always better.

No it's not always better both have there use
It's getting the right system for the user
And ps you may have 6bar incoming but then it's in to a pressure reducing valve then out to balanced cold supply's

 

[Ryan LPS]

Go biomass boiler with thermal store a instant hot water coil and a secondary hot return by far the best system for you in my op.... Government will pay you for the next 20yrs as well

 

[Kev the gas]

No it's not always better both have there use
It's getting the right system for the user
And ps you may have 6bar incoming but then it's in to a pressure reducing valve then out to balanced cold supply's

The 6 bar incoming was indicating that there is sufficient incoming pressure, obviously then reduced down.

I mentioned it just incase there was any doubt.

 

[Kev the gas]

Go biomass boiler with thermal store a instant hot water coil and a secondary hot return by far the best system for you in my op.... Government will pay you for the next 20yrs as well

Biomass even if mains gas is available??

Ive never heard that suggested before for a domestic property.

 

[Gray0689]

Go biomass boiler with thermal store a instant hot water coil and a secondary hot return by far the best system for you in my op.... Government will pay you for the next 20yrs as well

What's an instant hot water coil???

 

[Ryan LPS]

What's an instant hot water coil???

In thermal store you can get a coil that goes from bottom to top of buffer comes out around 76*c has to have a blending valve reli and yes why stay gas wen you can go green and still cut your normal gas bills today iv just put a small biomass pellet boiler in a small two bed cottage. Going to there vented cyclinder

 

[Gray0689]

In thermal store you can get a coil that goes from bottom to top of buffer comes out around 76*c has to have a blending valve reli and yes why stay gas wen you can go green and still cut your normal gas bills today iv just put a small biomass pellet boiler in a small two bed cottage. Going to there vented cyclinder

Lol that is the hot water coil
Instant hot water lol
It's only hot water if the store is hot lol

 

[Ryan LPS]

No they call it a install hot water coil cos it will work the same as a combi hot water on call constant. You may call it a hot water coil... Do you do many buffer systems then

 

[Ryan LPS]

Not being funny just wanted to no you views on it

 

[Gray0689]

No they call it a install hot water coil cos it will work the same as a combi hot water on call constant. You may call it a hot water coil... Do you do many buffer systems then

Yep do a few with buffer and a few with thermal stores
And never heard of a instant hot water coil
And no they don't work like a combi
As you have to have the store hot to get hot water the boiler or heat source heats the store direct
The hot water gets hot through heat transfer

 

[Ryan LPS]

Yh but most store are always kept hot as the pellets used to start boiler up and the to have on full burn to heat say a 1000L store what I installed with the hot water coil would take a fair amount of time but hence why there called a thermal store cos there always kept hot you wouldn't have a buffer system you would just have a standard unvented cylinder

 

[Ryan LPS]

Oh I said they work like a combi because through a coil it is instant hot water hence why I explained it like that maybe the wrong term of words but like I say I ment cos you can get instant hot water

 

[Gray0689]

It's only instant if the buffer or thermal store are hot yes correct to is better to keep hot all the time but in summer when no heating is required it's bad practice to keep a 1000l buffer hot all time
And a buffer tank is not the same as a thermal store
Do you fit many!!

 

[Ryan LPS]

The principal of a thermal store cylinder is similar to that of a buffer tank or accumulator. Essentially it is an efficient method of linking multiple energy inputs together, and provide domestic hot water as main pressure. Anyway I don't think it's fair to the o.p to carry this on. On his post if you wanna talk bout it mate then pm me....

croppie if you wanna remove are post up to are suggestion I think it's only fair that the o.p don't have us trying to get one over on the other

 

[Gray0689]

The principal of a thermal store cylinder is similar to that of a buffer tank or accumulator. Essentially it is an efficient method of linking multiple energy inputs together, and provide domestic hot water as main pressure. Anyway I don't think it's fair to the o.p to carry this on. On his post if you wanna talk bout it mate then pm me....

croppie if you wanna remove are post up to are suggestion I think it's only fair that the o.p don't have us trying to get one over on the other

Lol is that what your trying to do get one over on me lol
Nice to know anyway
No need to carry it on mate you know better
Thanks for teaching me about buffer tanks and thermal stores

 

[lame plumber]

personally I think a thermal store with boiler back up and solar panels would be a sensible option if you have mains gas. From what I have seen with pellet burners, most of the pellets are imported, and will soon rocket in price as demand increases and its hardly carbon friendly carting them half way round the world to the uk.

 

[Ryan LPS]

Mate I wasn't trying to teach any lesson I was just chatting....

 

[Ryan LPS]

Thanks lame plumber I agree lol

 

[Ryan LPS]

If you don't wont pellets then use wood chipping boiler or even log

 

[Ermintrude]

Why not replace gledhill with equally brilliant economy 7 instant water coil ? Why on earth would the op base any financial calculations on a British hash price? Could probably fit two pressurised cylinders and a boost pump, air heat pump new boiler and garden gate for same price!

Warning to OP when getting other quotes hide the BG paperwork and don't tell others you have had a BG quote as they will simply add on 5% because they know they will still be 30% cheaper!

 

[goldfrapp]

I recently took out a Gledhill systemmate hot water tank, massive rectangular box 250 ltrs of junk.

I installed a Worcester 42 cdi in its place and the flow rate to the showers has increased!

The Bg guy is correct regarding the softened water, Worcester will not allow softened water in their boiler, can a hard water supply be connected up to the boiler for the central heating side? It is ok for the domestic hot water side.

Thanks for the reply. Thats good to know you are getting good results with the Worcester.

I telephoned Worcester and they confirmed that CH side must be hard water (due to aluminium heat exchanger I think) but DHW side can be softened as heat exchanger is stainless steel. I can isolate the water softener so that the CH could be filled with hard water. But would the boiler still need a hard water supply ?

 

[Ermintrude]

If you don't wont pellets then use wood chipping boiler or even log

Don't forget air and ground pumps! Was in Slovenia they have some crazy log furnaces in domestic with massive thermal stores (thousands of litres)!

If you have a cesspit, stop using bleach and get an anaerobic digester, but with mains gas you probably got running water and all mod cons?

 

[goldfrapp]

Why not replace gledhill with equally brilliant economy 7 instant water coil ? Why on earth would the op base any financial calculations on a British hash price? Could probably fit two pressurised cylinders and a boost pump, air heat pump new boiler and garden gate for same price!

Warning to OP when getting other quotes hide the BG paperwork and don't tell others you have had a BG quote as they will simply add on 5% because they know they will still be 30% cheaper!

Getting another quote from local guy. Thanks for the replies.

 

[Gray0689]

personally I think a thermal store with boiler back up and solar panels would be a sensible option if you have mains gas. From what I have seen with pellet burners, most of the pellets are imported, and will soon rocket in price as demand increases and its hardly carbon friendly carting them half way round the world to the uk.

I'm not a big fan of solar on thermal stores
Simply because the householder generally just leave boiler heating store all time and solars don't get chance to work efficiently
And the pellets are made about 30 milled from where I live (ballcas)
I've fitted a couple of grant spirotec wood pellet boilers and must say very impressed with what I have seen so far

 

[Ermintrude]

Thanks for the reply. Thats good to know you are getting good results with the Worcester.

I telephoned Worcester and they confirmed that CH side must be hard water (due to aluminium heat exchanger I think) but DHW side can be softened as heat exchanger is stainless steel. I can isolate the water softener so that the CH could be filled with hard water. But would the boiler still need a hard water supply ?

No hard water through combi or any plate type heat exchanger causes scale. Phosphate type softness isn't best. That's why if over 200ppm you recommended to install cal mag or similar on combi!

 

[Mrs Tara Plumbi]

Getting another quote from local guy. Thanks for the replies.

Hi.
Do you want to tell us where you are - if any of the experts here might be able to give you a quote.

Back to OP - I'm a fan of combis! In my house we have a combi and 2 showers - I've never tried to use them both at the same time so I don't know what would happen.

but when I'm in the shower the kids frequently decide to come clean their teeth and flush the loo and wash hands - there is small minimal impact on the shower. But I'm sure you know incoming water pressure is important as well as the size of your boiler.

Finally, please be clear I'm not a heating engineer and the other guys on here write a lot of sense. If we had more space we probably wouldn't have a combi because my hubby also thinks along the same lines as the other heating engineers.

 

[lame plumber]

I'm not a big fan of solar on thermal stores
Simply because the householder generally just leave boiler heating store all time and solars don't get chance to work efficiently
And the pellets are made about 30 milled from where I live (ballcas)
I've fitted a couple of grant spirotec wood pellet boilers and must say very impressed with what I have seen so far

then the installer hasnt set it up correctly and explained how to use it properly, whats cheaper and better sun light or pellets made from chopping down a tree, grinding it into a mash, forming pellets and then moving the end result to the customer and burning it and producing co2. sometime the world will see snese and go for the option that relies on sunlight with a backup mechanism and not vice versa!!

 

[Dotty]

Thanks for the reply. Thats good to know you are getting good results with the Worcester.

I telephoned Worcester and they confirmed that CH side must be hard water (due to aluminium heat exchanger I think) but DHW side can be softened as heat exchanger is stainless steel. I can isolate the water softener so that the CH could be filled with hard water. But would the boiler still need a hard water supply ?

The heating side would yes, but get the filler loop tapped off before the softener and the job's a good'un!

 

[Dotty]

The principal of a thermal store cylinder is similar to that of a buffer tank or accumulator. Essentially it is an efficient method of linking multiple energy inputs together, and provide domestic hot water as main pressure. Anyway I don't think it's fair to the o.p to carry this on. On his post if you wanna talk bout it mate then pm me....

croppie if you wanna remove are post up to are suggestion I think it's only fair that the o.p don't have us trying to get one over on the other

I'll leave it running Ryan, It's an interesting exchange of opposing views and doesn't come across as one upmanship. As long as it's kept friendly then I'm cool.

 

[Gray0689]

then the installer hasnt set it up correctly and explained how to use it properly, whats cheaper and better sun light or pellets made from chopping down a tree, grinding it into a mash, forming pellets and then moving the end result to the customer and burning it and producing co2. sometime the world will see snese and go for the option that relies on sunlight with a backup mechanism and not vice versa!!

No set up correctly at start explained correctly
But some customers always think they now best lol

 

[smhstu]

Why not get a combi three zones one for a cylinder coil on vented cylinder fed by tank to a pump just for showers and have instant hot water for all other outlets?

Just a suggestion to put the cat among the pedgons..

 

[nialle17]

A system boiler would enable you to make better use of the showers and baths you have. A combi would defeat the object of having numerous showers and baths if they cant be used.

 

[Howsie]

Why not get a combi three zones one for a cylinder coil on vented cylinder fed by tank to a pump just for showers and have instant hot water for all other outlets?

Just a suggestion to put the cat among the pedgons..

There are many ways to skin a cat depending on the cat. TBH if its a decent size house, it should have secondary return anyway.

 

[Gray0689]

There are many ways to skin a cat depending on the cat. TBH if its a decent size house, it should have secondary return anyway.

Agree most do just depends on location of cylinder to bathrooms

 

[Jimbob]

Combi on that lot is always going to be insufficient. Any manufacturer would also agree. Stored DHW is the only way to go. Don't be scared by BGs price, they will be much more than a decent local installer.

 

[Centralheatking]

I will not read the comments below - but really a combi will not do they are rubbish and
go wrong esp in this set up.

All the sensible tradesman below will tell you to fork out for a decent system set up
you could even be lookin at a dual boiler system in my opinion

CHK

 

[Centralheatking]

Mike is correct get a BG quote and we normally half it and still make a good wedge

I agree, go for an unvented and system boiler. get alternative quotes from a xouple of local guys and the price will be a lot less than the Bg price.

 

[Kev the gas]

I will not read the comments below - but really a combi will not do they are rubbish and
go wrong esp in this set up.

All the sensible tradesman below will tell you to fork out for a decent system set up
you could even be lookin at a dual boiler system in my opinion

CHK

What a fracking stupid waste of internet space.

If you cant be bothered to read the previous discussions, why bother to comment?

 

[Ermintrude]

I will not read the comments below - but really a combi will not do they are rubbish and
go wrong esp in this set up.

All the sensible tradesman below will tell you to fork out for a decent system set up
you could even be lookin at a dual boiler system in my opinion

CHK

Combi rubbish not in right application? Agree wrong for this set up, ACV cylinder and high output system boiler with water softener on DHW & DCW excluding potable water. Get cylinder with solar flanges for future?

Also possibly zone floors ?