Some Combi boiler questions

[Dave Plowman (News)]

Well, an auto has many advantages. A combi only saves some installation space and possibly initial cost. But can never, in practice, perform as well as a decent storage system.

[Owain]

"Paul Giverin" wrote | >> I'm thinking about replacing my back boiler with a combi boiler. | >> The reasons are mainly about space. | >I'm sure that you've gone into all the pros and cons of switching | >to a combi boiler but I have to say that I wouldn't touch one with | >a barge-pole.

One of their drawbacks is that you usually lose the back-up of an electric immersion heater.

| I don't mind spending what it takes to get a good quality boiler | which is large enough to give me a decent flow rate.

First thing is to check your cold water flow rate is adequate, usually measuring litres per minute with a bucket at the kitchen tap.

An alternative to a combi might be a wall-hung boiler and a mains pressure hot water cylinder (which does not need a tank) in the loft. Gets the cylinder out of the downstairs toilet space whilst giving you stored hot water. If the circumstances are right you might even get the boiler in the loft too.

Owain

[BrianW]

Rather like many of the posters to this NG then.

Brian

[JNugent]

Well you see, Brimstone, running a combi boiler is very much like making love to a beautiful woman...

[Mark Hewitt]

It has the advantage of never running out of hot water. Our problem was that the hot water tank was just big enough to fill the bath,, and no more. Anyone did any washing or anything and you'd end up with a shallow bath.

Our combi failed this morning, pressure was down to zero, turned the valve to turn the pressure back up again.. not sure that is supposed to happen :-\

[Dave Plowman (News)]

Then you need a larger cylinder - or a second one. Fast recovery types will also help.

[Mark Hewitt]

We had no additional space for such things. In any case we had to replace the whole system as it was 40 years old and worn out. A combi system cost about half that of a traditional one, and we now have a lot more space in the house too.

[Dave Plowman (News)]

Yes - if space is tight then that is their main advantage.

Well, replacing a worn out storage cylinder is hardly expensive. The pipework will have to be altered if changing to a combi, and to do this properly could be expensive. If you simply plumb the combi into the old hot water pipework, there will almost certainly be longer runs than needed, unless the combi goes where the old storage cylinder was - unlikely.

Of course if the original system was poorly designed or installed it might well be cheaper and better to start again.

[Sleeker GT Phwoar]

What, if things go dry, it's game over?

[Mark Hewitt]

The problem wasn't so much the boiler or the cylinder but just that the rest of the thing was so clogged up with crap that just replacing one part of it wouldn't do the job. So a complete replacement was needed,, which we didn't enter into lightly, we tried for 4 years with replacing parts but in the end couldn't make it work.

At least we have a good system now.. Albeit with some noise problems, which I'll jump over from uk.rec.driving to uk.d-i-y to ask about :-)

[Christian McArdle]

A modern rapid recovery storage system also never runs out, if you draw water as the same pathetic rate as an instantaneous combi. Older types have low efficiency heat exchangers that can't accept the full output of the boiler. There's no excuse in a modern system, though.

Christian.

[Kev (The Car Collector)]

Cant say I agree with that one - I had one installed in my mothers house along with a Myra Power Shower and it was great. No problems filling a bath but it would depend upon the capacity of the boiler unit for the time taken to heat a certain volume of water to a given temp. I thoroughly recommend them.

Kev

[Kev (The Car Collector)]

Yes, it does drop after a while - the system isnt totally leak proof. Dont worry about it :)

Kev

[Mark Hewitt]

I'm not worried about it now.. I just need to remember to take a look at the pressure gauge from time to time to make sure it isn't too low, and top it up if need be.. Mind you I've no idea what do to if it is too high. I don't believe we were furnished with an operators manual.

[Dave Plowman (News)]

Sounds like it never saw inhibitor - and or was pumping over etc.

Do make sure your new system has inhibitor. Not using it is rather like filling the cooling system in an ally engine car with plain water - a recipe for disaster in the future.

[Dave Plowman (News)]

The problems usually are in the winter, when the incoming water is at its coldest. It's also not just a question of the boiler size, but whether the incoming water supply is up to it. Some may have to upgrade both this - and even possibly the gas main - to get a really adequate performance for a family house. Which adds very considerably to the cost.

[John Rumm]

If it drops by much, and does so frequently, then you really *should* worry about it! All that water is going somewhere and it would be a shame to find it feeding dry rot in some warm dark corner of your house. Not only that you will be slowly diluting the corrosion inhibitor out of your heating system, which will lead to problems later with that.

[Mark Hewitt]

I've no idea what an inhibitor does or what it is for or where it goes... etc. So I have no idea if my system has one.

[Clive George]

I think it's probably a very good idea that you go and find out about this, otherwise you will knacker your nice expensive CH system.

"fernox" is a good word to start with.

cheers, clive

[Set Square]

You don't have *one* - you have *some*!

It is a liquid which prevents corrosion by stopping the water in your system from reacting with the metal radiators and pipes.