Replacing Conventional with Combi Boiler - How DIY is this ?

[Kevin]

I am considering replacing my conventional boiler with a combi-boiler and during the replacement I will probably also relocate it. One option is to move it on the same wall but closer to the origin of the pipework, i.e. I will only need to cut the existing pipework not introduce any new joints except where they actually connect to the boiler. The other option is to move it onto the opposite wall which will involve new pipework.

I have done plumbing before and am reasonably confident but for obvious reasons I am a little wary of messing around with Gas. The controller is also fairly old and will need to be replaced. Also there are no room thermostats although I have fitted thermostatic valves to every radiator, so do I actually need one ?

If possible I would like to do most of the work myself and get a CORGI man in to do the final connections into the boiler. Any ideas how realistic this is ? Can I re-use the existing pipework or will I have to run new pipes throughout the house ? Do I still need a separate pump or will this be built into the new boiler ? Should I consider doing this in two phases, i.e Central Heating first and Domestic Hot Water second ?

I'd like to minimise the amount of time we are without hot water/heating. Anybody aware of any web resources which may advise the best approach (i.e. order of activities) ?

[Christian McArdle]

You need what is termed a boiler interlock. This means that once no heating is required, the boiler must be turned off. This can be done in two ways. Firstly, you can have a room thermostat in one room with no TRVs. Secondly, you can have an automatic bypass valve with a flow switch. When the radiators are all off, the automatic bypass opens, the switch trips and the boiler turns off. Some logic must be incorporated into the system to notice that the valves have opened again, though.

You can. Finding the CORGI can be problematic.

Modern condensing and combi boilers frequently have internal pumps. It is by no means universal, though.

You could do this. You could also use the combi section for the kitchen and shower and maintain stored water for the bath for higher flow rates.

Christian.

[Andy Hall]

Yes you do. The best solution is to put a room thermostat (ideally with time controller and night setback) into a location such as the living room, dining room, hall or landing. Either remove the TRV on the radiator in said location or fully open it. You don't want to have the TRV of that radiator and thermostat both in operation, or the temperature in the rest of the house will tend to wander all over the place.

It is, but it would be prudent to find one that will agree to do it first. That may or may not be easy. Some CORGI people are reasonably relaxed about doing this as long as they feel that you know what you are doing, others won't because they are taking on a responsibility or simply for commercial reasons. Getting the flue right in terms of location and seal is as important as the pipework.

Generally, if the pipework and radiators are in good condition, they can be re-used. Normally, you will be converting the system to pressurised operation. This is not difficult - some components may be built into the boiler - but you may create seepage at radiator valves and need to replace or tighten them. Refer to Ed Sirett's FAQ on sealed systems.

Typically it is built in. If not, and the pump is not recent, then replacing is a good plan.

As part of the upgrade, giving the system a very thorough flush is important (see other posts for a method that I have used) and fitting a strainer to the return is a good idea too.

Have you sized the combi to be sure that enough hot water is being produced for your needs? If you have a separate bath and shower, then a large model is needed. Before you do anything, check the mains water flow rate at the kitchen cold tap. Then measure the flow rate at bath taps and shower. Bear in mind that a combi boiler is rated for a 30 or 35 degree temperature increase. This means that in the winter when the water may only be at 8 degrees or so, the *total* water for a shower will be the spec. figure for the combi. A small one at 11 litres/min will be disappointing in most cases.

You could proceed in stages. For example, you could keep the HW cylinder in place and contine heating it with the boiler or even an immersion heater. Then fit the new boiler and rejig the hot water pipework last.

I would tend to do what is needed to keep the hot water in service. You can always warm rooms with a fan heater or something. Absence of hot water is a major pain.

.andy

To email, substitute .nospam with .gl

[IMM]

First, How many baths, showers, size of house, etc. Do you intend to take a lot of baths? There are low and high flowrate combi's.

[Big Phil]

I'm about to do exactly the same thing. I'm replacing an old conventional boiler in the basement with a Condensing Combi in the loft (with suprising little extra pipework required!)

The boiler I'm going to install has a built in by-pass so I'm going to fit a TRV in every room, then when there's no demand the boiler will turn off until there is. Since this is part of the biler all the logic to turn on again etc. is built in. I've chosen a Vaillant EcoMax828 which is pretty pricey, but good quality and has everything built in.

Again, this is my plan. Although I already know a CORGI registered plumber who is happy to just pop round to check my pipework and connect to the meter.

I'm planning on reusing the existing, including reusing the current boiler's 22mm pressure release pipe to take the gas up to the loft.

I'm taking a few days off work to do this and will get all the pipework in place so that once the old system is disconnected I hope to get the new one up and running in a day. I'll leave the old system physically in place though, just in case I need to reconnect for any reason!

Good luck. Let us know how you get on.

[Nick Finnigan]

Just to tag on a question which Kevin might need to consider... what are the best options for routing a gas pipe from one side of the room to the other (particularly past a doorway)?

[Kevin]

For me this is not an issue, my boiler is located in the utility room and the pipework is surface mounted close to the ceiling hence easy to get at. When I have finished all of the work I need to do in this room, I might consider boxing the pipes in but in this particular room the fact that the pipes are surface mounted isn't really an issue.

[Keithc666767117]

everything is done by the combi ...connect heating flow and return, domestic hot and mains in and gas connection. Combi will contain all controls required to deal with systems. However it is not recommended that you get corgi person in to do final connections I am a plumber myself and would not do this as requirements by law dictate otherwise ....advice only.....