changing normal boiler to combi

[Big_T]

hello,

I currently have an ideal 2000 boiler doing my central heating and hot water. It only has 3 pipes going to it, i assume gas outlet and return. I have a motorised valve in the airing cupboard, with a common and two outlets, one side for heating the other for hot water. I am assuming that my hot water is heated through a coil in the tank because I only have 2 water pipes coming out the boiler. I also have 2 big water tanks in my roof space, and an electric pump in the airing cupboard.

what I want to do is convert to a combi (been told Worcester are best?).

I THINK thank the heating side of it will be fairly easy, use the existing two pipes I have from the boiler, take out the 3 port valve and just connect the common to the heating side, and completely remove the hot water side and my expansion tank.

does this sound ok so far??

As for the hot water, this is what im most unsure about, the boiler is mounted fairly close to my kitchen sink, so would it be possible to take the cold water supply from the supply to the sink? and as for the hot water out, could i just T into the hot water pipe to the sink and then that would charge the whole hot water system???

I hope this is how it could be done, if not then its going to be a major job. Could someone please tell me what they think about this, am I on the right lines or does it need to be done another way?

Any help will be greatly appreciated

Cheers

 

[chrishutt]

Your on the right lines....but 3 things...

1. You will also need to remove the existing pump, since a combi will have an integral pump.

2. The existing hot water pipework will be partly in 22mm tube, which is rather too big for a combi hot water supply. It will take longer for the hot water to displace the larger volume of cold water in 22mm pipe, hence slower time to reach hot taps.

3. It's important to thoroughly clean the existing system before running the new combi. There are various techniques for doing this which you will need to research.

 

[Big_T]

thats great, thanks alot for your answer.

couple more questions though if you dont mind

would it be possible to leave to 22mm tube but get a bigger boiler to cope with it?

does the cold water pressure going in determin the hot presure going out or does the combi have 2 pumps, one for heating and other for water?

I have heard that you need to keep 1 rad just open a bit all year round, is this true?

many thanks for your help so far

cheers

 

[Bahco]

Would it be possible to leave to 22mm tube but get a bigger boiler to cope with it?

Seems a bit drastic, If you leave it at 22 mm your water will be cooler at the taps as well as a reduced flow.

Cold pressure in does affect what comes out as hot, and you only have one pump.

You do have to have a bypass installed OR one rad perm open

 

[Gasman1015]

You do have to have a bypass installed OR one rad perm open

No OR's about it , you need an automatic bypass.

 

[gazthepottertonengineer]

You do have to have a bypass installed OR one rad perm open

No OR's about it , you need an automatic bypass.

Not neccessarily you will find that alot of combi boilers have integral bypasses built in which does away with the need of any type of external bypass

 

[Bahco]

I have seen one rad left as a bypass a few times on the £1800 installs.

Even seen no roomstat fitted.

 

[kevplumb]

well you should have fitted one naughty boy

(wheres proscotts phone no)

 

[Gasman1015]

You do have to have a bypass installed OR one rad perm open

No OR's about it , you need an automatic bypass.

Not neccessarily you will find that alot of combi boilers have integral bypasses built in which does away with the need of any type of external bypass

You know that and so do I, but not all boilers have one, all I said was he HAS to have an automatic bypass, some times boiler bypass is inadequate for the system and require external one at least 1.5 metres from boiler and Worcester have recommended this on certain models.

 

[Big_T]

Would it be possible to leave to 22mm tube but get a bigger boiler to cope with it?

Seems a bit drastic, If you leave it at 22 mm your water will be cooler at the taps as well as a reduced flow.

Cold pressure in does affect what comes out as hot, and you only have one pump.

You do have to have a bypass installed OR one rad perm open

Thank you for your help

It might seem a bit drastic but I dont think its as drastic as changing all the pipes, that would be a major major job, id rather pay a couple of hundred more on the boiler than a couple of thousand on replacing the pipes. I also have very high cold water pressure, would this help?

 

[Bahco]

Won't cost much just to replace the hot pipe (22mm) to your taps. The boiler is next to the sink after all.
Just a case of running the hot 15 mm to your upstairs bathroom.

 

[Gasman1015]

In some cases, you will find that the kitchen is fed by 15mm, which has been teed from the bathroom.

 

[Agile]

I think that even Potty probably say that an external by-pass is needed EVEN if their boiler has an internal by-pass.

The energy efficiency courses ( inc the Potty ones* ) always stress that an expernal one is required regardless.

Tony Glazier

 

[Big_T]

Won't cost much just to replace the hot pipe (22mm) to your taps. The boiler is next to the sink after all.
Just a case of running the hot 15 mm to your upstairs bathroom.

its going to be a bit more than that, the pipes run under my newly tiled kitchen floor, throught the hall then up from the downstairs toilet to the bathroom upstairs. so it will be quite a major job, so if i could get away with a bigger boiler and the fact that i have very hight cold water pressure?

could someone possibly recomend a boiler, possibly a Worcester, that would cope with 22mm and run 8 rads (9 if i need one on all the time)

cheers

 

[Agile]

If you read the answers again and think about it, the size of the boiler will not solve the problem of waiting until the water runs hot from the tap.

I do have to wonder who suggested tiling over pipework when you were not satisfied with the plumbing and particularly were contemplating a replacement boiler.

Any boiler will run your rads, the boiler power is required to heat the water.

Tony Glazier