Will our shower work with combi?

[brettjbuckley]

We have a traditional Ideal Mexico boiler and we are considering updating the heating system and replacing with a combi.

The advantages, apart from efficiency, are that we would lose the cylinder & header tank and also move the boiler from being in a kitchen cupboard to the spare wall in the cupboard under the stairs, gaining us more kitchen space.

We have had two plumbers quote for the work and both have pointed out that our Grohe shower is not designed to run off a combi (currently is fed with a pump and a header tank). Whilst both plumbers suggest thta it will "probably work", neither can gurantee it and one suggests that in the worst case scenario, we may need to replace the shower too, but that we will not know until afterwards.

Has anyone else had experience of fitting a combi on a shower needing a header tank and pump??

 

[breezer]

I am not a plumber, but from what i read it wont work because you wull have to pump the cold water side to match the hot flow which is against the law (to pump directly from the mains)

also how many in your family, combis are good but not marvelous if 3 or more in a family

 

[kevplumb]

is it the "chrome bar with a knob at each end" ?

 

[brettjbuckley]

No, the shower has a brass panel with two large brass knobs.

 

[ChrisR]

Breezer's concern is bypassed if you lose the big cold tank, so both pipes will be high pressure.

His concern over your satifaction with a combi, though, isn't! Go for one with a very good hot water performance - at least a 28kW. First all the plumbers who came to your house will have tested your mains pressure and flow of course so we assume that's OK ?? DO NOT hope for the best on that one.

I can think of 2 installations where the combi output was OK on the pumped shower (not pumped any more of course) and one where it wasn't - could have been a bigger pump beforehand.

Depending on the model of your mixer you may be able/have to change its cartridge (assuming it's thermostatic).

 

[brumylad]

My tuppence worth:

Keep your existing boiler

put an unvented hot water cylinder in the cupboard under the stairs

remove old HW cylinder and cold water cistern.

will cost about the same and leave you with a better system plus less to go wrong.

 

[kevplumb]

assuming 22 mm feed to said

 

[brettjbuckley]

Would it be pointless to keep the header tank just for the shower such that there would be a guarranteed pressurised cold water feed? Our main concern in all of this is that our shower works superb at present - probably also because we have a pump between it and the cylinder (which I presume a good combi will do for hot flow).

 

[PEDANTICVINDICTIVEMAN]

I reckon your shower will work ok with a modulating combi, go for a 28 or 35Kw as Kevplumb said, both inlets will be mains pressure so should balance ok.

 

[brettjbuckley]

We spoke to the plumber again and he basically confirmed that no combi would ever supply a shower as well as one like ours that is pumped from a cylinder / header tank. He said that if it was done right then we should still have a "decent" shower. Of course, none of us will know until the combi is in and it's too late. Then I'll have my partner on my back who absolutely loves our shower!

So, my understanding is that to maximise our chances of retaining a decent shower, we should get a decent combi (35Kw+).

If we do have to change the shower cartridge, is this a major job? I'd like to think that we could do it without disturbing the outer appearance of the shower which is all neatly tiled in and has the brass Grohe control panel.

Anyway...why change the shower cartridge all? Isn't it all about water pressure or I am being really naive here?

 

[brettjbuckley]

Well, folks, here is the conclusion...

Our Baxi 105e combi was installed 2 weeks ago and all works perfectly - including the shower which is now much more powerful than it was when previously fed from a pump and header tank arrangement. It actually hurts your head to stand under it.

T'other half is happy and I'm happy as I've lost a header tank and cylinder and gained a big cupboard too.