Whats involved in replacing a condensing for a combi.

[FrankE]

I'm planning (when i have funds) to replace the existing boiler (Ideal Stelrad 2000 Yplan configuration) with a Combi boiler.

I'm of course getting an approved contractor in to do it but I just would like to know what's involved and how much of the Y plan system can be retained.

Would it be possible to find a boiler that is retrofittable onto the existing flue wall peneration?

Can they just cut off the CH Flow and Return and pipe those back up to the new boiler?

 

[stem]

Looking at your subject title, I think you are getting your terms confused. All boilers installed now are condensing boilers, combi or otherwise. Under the correct conditions, they are able to extract the maximum heat from the gas you burn.

As well as providing central heating Combi's have additional (more complicated) internals that provide hot water without the need for a separate hot water cylinder, and the cold water storage tanks above.

In your situation, unless you have a desire to get rid of your existing hot water cylinder, you could have a new standard condensing boiler (just as efficient as a combi but without the extra hot water parts) and keep the existing "y" plan in it's entirety including pipework tanks and wiring, it would be a straight swap for the boiler you have now. You would probably have to modify the wall for the flue, but that's a minor issue really, easily made good by a professional. You would also need a condensate drain pipe adding but both of those apply to a combi too.

If you install a combi, all of the tanks will have to go, the existing controls and motorised valve will need removing, you will need a main cold water supply piping to the boiler and a connection feeding the hot water taps. Also, because combi's produce hot water instantaneously they have bigger burners which often means they need a larger diameter gas pipe installing between the gas meter to the boiler.

Combi's are nice for new builds as they avoid the time and cost need to install a hot water cylinder and the associated tanks. Also the wiring is also much simpler. But if you have these already that advantage is lost.

Horses for courses really.

 

[stem]

Ignore this post, wrong button

 

[FrankE]

The kitchen is small L shaped and lacking in unit space and free worktop, so I'm very keen to get rid of the HW Cylinder and CW tank, which is at the top of the L .

The cupboard it is in isn't used for airing so would give an additional unit space for and more worktop space on the 'upright of the L' for futting in a 600mm induction hob (currently 500mm freestanding (broken) cooker. Along with removal of the cupboard, taking out the fridge freezer next to it and putting in separate fridge and freezer under the worktop would liberate two unit widths of worktop space.


Removing the pump and valve then plumbing round the back of the unit which spans the toe of the 'L' would free up the bottom half of a double unit where all this resides just now. Most f the stuff that in the cylinder cupbord would go in there.

The existing wiring is untidy anyway, the (mechanical Randall 102) timer is in an awkward place so it's no loss. Theres a directly wired fused connection unit ready for it and provision for an external programmer at a convenient location has been chased in.

Not much HW is used. I have an electric power shower, no bath so only really use HW for 1-2 bowls of dishes in the evening, hand and face washing and 1-3 economy loads of laundry a week. CH&HW is on an hour in the morning and a couple of hours at night, most of the HW isn't used.

The wiring and the plumbing from the load side of the valve goes under the bathroom which the installer tiled over without leaving provision for getting under the floor ask asked so there i s no further access without ripping up the floor or digging out the void and knocking out a spice in the dwarf wall.
The gas pipe goes through there too. It's 15 mm. For a 2 bed flat which is well insulated (DG, ext doors not draughty, partial underfloor insulation [WIP], cavity wall insulation, ceilings partially replaced with 2* 15mm acoustic board WIP) Might be tricky getting a gas pipe to the boiler location. Only other gas applicance is a gas fire which is never on except when the GCH fails.

If I get the system up and running again I may have a new programmer put in with separate CH and HW boosts.

Given size of place woulld a 22mm gas line be required.
The condensate drains to?

 

[stem]

OK then makes sense to ditch the cylinder & tanks.

With a combi, it's more the hot water, not so much the size of the property that determines the boiler size and hence the gas supply. The boiler needs to heat a usable quantity of cold mains water at say 5 degrees up to 65 degrees in a few seconds as it passes through the boiler. Even small properties usually have 30kW boilers to generate a reasonable flow of hot water, but the heating demand may only be 6kW. So I would say almost certainly you would need 22mm pipe. But your installer would have to calculate this properly.

The FCU sounds OK. If you were to buy a boiler with the programmer built in, then apart from a cable to the room thermostat you would only need one 3 wire connection from the FCU to the boiler. Having said that, some boilers have an integral receiver and come with an rf thermostat so no thermostat wiring is required at all.

You can fit an external programmer if you prefer, but this would need extra wiring.

The water from the condensate drain can be piped, using small diameter (overflow) pipe into the normal waste water pipe, or to a drain or soakaway outside. If the pipe runs outside, because it contains only a small amount of condensate intermittently, it will need to be insulated to stop the condensate freezing in the winter.

 

[FrankE]

Thanks, that gives me an idea what is required during installation and which fixtures would need to be removed for the installer.