I am thinking about replacing our gas central heating boiler and am wondering how big a DIY project this would be. I have moderate DIY experience and skills. In its simplest form I guess that I would need to remove the old boiler and modify the connections (gas, electricity, water in, water out and flue) to connect them to the new boiler. Is this too simplistic? Are there obvious pitfalls that I should be aware of? Any comments and advice gratefully received! Many thanks.
If you don't currently have a condensing boiler, you will need to organise a new drain. Preferred method is to run this inside the house into an existing waste, because drains going outside can freeze in winter, especially if the guidance isn't followed exactly.
But no, if you are comfortable with all the elements it shouldn't be too difficult. You do know the rules about gas? Check the FAQ.
My personal tip is to include lever-operated full flow ball valves so that you can isolate the CH pipes and cold water supply, because the built-in ones are generally inaccessible, difficult to operate, and end up leaking.
The complexity varies a bit depending on what you are swapping for what. For example replacing one combi with another is usually fairly straight forward, but converting to or from a storage based system requires a fair bit more work.
You may need a few unusual tools like a core bore for cutting a new flow exit (note if changing from conventional to condensing then the flue, even if the same size, is usually cut at a slight downward slope for a conventional boiler, and a slight upwards one for a condenser). You will need a manometer for doing the gas soundness checks.
To add to other comments, it would be worth checking the size of pipe feeding your current boiler and whether it has other "users" teed off the feed. It may be necessary to increase the size or provide a dedicated feed from the meter.
I'd not include any isolating valves other than for the cold supply - which is mandatory anyway. The thought of the boiler firing with those closed would worry me. Rads can be removed by closing their valves. If any other work is needed so you have to drain it all down - a good time to replace the inhibitor.
I did mine 10 years ago, except I was also installing all the central heating, so it wasn't a swap, but a brand new system. I was already proficient at soldered plumbing, and I had read and understood the gas safety regs before starting, and relevant building regs. (Actually, I made it all conform to Part L even though it wasn't yet in force.)
As others have said, you will have to use a condensing boiler now. Any new boiler isn't going to be able to use an old boiler's flue. You may need better controls than you have, such as some type of boiler interlock to switch off when there's no call for heat (e.g. a room stat and H/W cylinder stat if you are keeping a H/W storage cylinder), zone valves and/or multiple heating zones, etc. You may need to convert the system from vented to sealed (as I doubt you can get boilers for vented systems anymore - they were rare 10 years ago). You might also want to think about radiator sizing to make more efficient use of a new condensing boiler, although that's not a regulatory requirement.
The hardest part of the whole installation was lifting the boiler (45kg, IIRC) up a ladder and hooking it onto the wall bracket, particularly as I had decided to have it high up on the wall. I did a few practice lifts, and decided that if it started falling in some direction out of my control, I would simply let it crash onto the concrete floor and buy another one - I wasn't going to risk a back injury in some fruitless attempt to save it, for the sake of £600. Fortunately, I managed to get it onto the wall mountings OK. You might want to choose a boiler which is a one man lift, or choose a location where you can fit two people in to lift it.
For the commissioning, I ended up buying a flue gas analyser. I get the impression this isn't needed for most boilers nowadays though, and many gas installers don't have one. (It wasn't supposed to be needed for mine, but several of us here who used the same boiler found the factory pre-adjusted mixture which you weren't supposed to need to adjust was actually miles off.)
My boiler came with isolating valves to fit on the flow and return, to allow the boiler to be maintained without a full drain-down.
I fitted 2 zones, and each has a pair of isolating valves so that if it did spring a leak, I can isolate it and keep the rest of the heating working. They were also used because I didn't actually install the downstairs zone until a year after the upstairs zone. However, not having used them for some years now, I have found they don't turn anymore, at least, not without using sufficent force that I might break them (they are 22mm full bore valves).
I did this but took the precaution of having my mate alongside who is GasSafe registered
I took the view that it was best to be on the right side of the law and do all the hard graft and get him to do only the connection In the end it was a good balance as he was more skilled and it saved time
I researched and a Remaha boiler was the best at that time (about a year ago)
I needed to get the last one I did on a wall in the corner of the room over the kitchen worktop - where the worktop spanned two utility spaces and hence was not really up to being stood on. I found the safest way was to pile up tool cases on top of the worktop, and then get the boiler up the ladder such that I could dump it on the tool cases. They were slippery enough to allow it to be slid so that its back was to the wall
- just a tad higher than its mounting lugs on the back plate. Then held it with one hand and slowly pulled out one of the tool cases in the middle of the stack to lower it into position.
In the end I trusted the warnings in the manual on mine that said "do not attempt to adjust" etc... ;-)
Many thanks to those who have taken the trouble to answer my question so fully. The comments have been very useful and interesting. I'll now think about whether I am brave enough to go ahead with this project! Thank you.
From the questions you're asking I'm guessing parts of the job are likely to be outside your competence. I'd strongly suggesting phoning or emailing around local Gas installers and finding one who would be happy to work with you on this project, where they do the bits they need to be sure of and you do what's in your scope. But get someone on board first: if you get part way through the job and have to call someone in to sort it out it could end up costing more than if you'd got them to do it all in the first place.
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