Replacing conventional boiler

[NotAllIndividuals]

We have an old old conventional boiler that works fantastically well but we are doing a lot of revamping work so are thinking of updating to a combi. A plumber told us we'd need to replace all the pipework to prevent any black radiator gunk damaging the new boiler. A friend say no, that's rubbish, their pipes were flushed when their system was switched.

Anyone experienced this and knows who is right, or if there are tests to see if pipes need replacing? It makes a bit of difference because we won't do any decorating until after the switch if all the pipework has to be replaced. Unfortunately there's no thermostat on boiler or radiators so we do want to do something sooner rather than later, just not sure what.

We've just spent some time looking in to this for mil. Pulling together various plumbers views, plus what we had read

• combi conversion was considerably more expensive than replacing with a shiny new regular boiler
• most people recommended at least a chemical flush
• they weren't planning to replace her entire system although there would have been some repiping around the tanks
• because the combi is pressurised and the current regular boiler setup isnt, there is a risk of developing a leak somewhere. All her pipework is about 40 years old and has never been pressurised.

We did a combi conversion on a previous flat and did end up replacing everything as we needed lots of extra rads and changed the boiler location so it was easier to just strip and start fresh

Are the pipes copper or steel? Check with a magnet.

Why do you think a combi would suit you better?

How many bathrooms/showers do you have, and how many people are likely to live in the house?

Combi systems are sealed rather than with an expansion tank. If your plumbing is 40 years old just replace it. You’re likely to spring a leak.

If you are doing revamping anyway just replumb your CH. If cost is the issue then you can take the risk but it will be even more expensive if it springs a leak and you have to replace the piping after you’ve finished the building work that was going on as you’ll have to redecorate again as well.

Timing is more the issue than cost, we want to get on with it but also planning an extension which might take a while. I'm trying to get the sequencing right so we don't go back on ourselves, which logic says wait til after extension is done but impatient little me wants to crack on and get some stuff out of the way asap.

Pretty sure the pipes are copper from what's visible but will check, does that make a difference? Water isn't hard in this area. There are two adults and a baby and no plans for any more! One bathroom and although we might add a second it would have electric shower. Im more familiar with combis and all the advice online suggests they're more efficient but happy to be corrected. To complicate matters I was looking into solar hot water that could only be added to conventional system. We could look at like for like replacement in that case. Boiler has a service sticker from 1985 inside cover so guessing it's around that age so it will either keep going forever or breakdown in the height of winter according to sod's law.

Most modern boilers are sealed, but not all are combis.

Conventional regular boilers are still available. They are not sealed or pressurised and are simpler so have less to go wrong.

All modern boilers are "condensing" and more efficient on use of gas, regardless of being combis or conventional.

Combis are very suitable for small homes with one occupant. As home size and number of occupants increase, they become less ideal.

I've been looking at boilers too as ours is a conventional boiler with tanks in the loft. Would a sealed system boiler be best in our case as we have 1 bathroom, an ensuite and a downstairs toilet - 2 adults, 2 kids? Have heard combi isn't the best for multiple bathrooms

dementedpixie from what I understand it's to do with the flow rate you need, number of bathrooms is a proxy for that but a poor one IMO. A tank full of hot water stored from a conventional boiler can give you a lot of hot water fast, but when it's gone it's gone. A combi will give you a smaller flow but on demand. If you try to use everything at once a combi won't keep up and someone will be dancing under a cold shower! Down side of conventional system is you're heating water you might not use so you wasted that energy. I would think that with some tinkering once you get to know your patterns you can make either work for you.

I think that's what I need to do - sit down and work out when and how much water/heat we need. The online calculators make assumptions that maybe don't apply to us. And if I can justify keeping the conventional boiler I can seriously look at adding in solar, which I'm keen on.

Last question - given that the boiler is at least 30 years old would we be mad to not replace it when we're doing all the other work? I don't want to do it for no reason but equally I don't want to finish tarting the place up with new carpets only to be faced with upending it all to replace boiler, pipes & rads.

Thanks all, plenty to think about that really moved away from my original question. It's hard when you don't know what you don't know!

A system boiler with a (preferably unvented, if your incoming water flow is sufficient) cylinder would be suitable.

Modern practice is to use larger cylinders, often 250 litres or so, which can do a couple of baths or multiple showers or a whole day's use without running cold. This is the most economical way, as the boiler only needs to be timed "on" once or twice a day. Running a boiler for multiple short periods (like a combi) is less economical, because you are repeatedly heating up the metal and pipes, only to let them cool down again.

A vented boiler is simpler and has less to go wrong, but needs more attention paid to the corrosion inhibitor, as water is exposed to the air in the F&E tank, and there are pipes in the loft that might freeze.

One other thing to consider - do you currently have an immersion backup for your hot water?

This has been a factor for MIL; at the moment she has regular boiler and an immersion backup. Her boiler is dead, totally, heading off to boiler hell. It's taken a while to get people out to look at the old one, confirm it's dead, get quotes for replacements, get replacement booked in...by the time all is said and done she'll have been boiler-less for 3 weeks. Having the immersion (plus a couple of electric heaters) has meant she could stay in the house.

When our combi died a few years ago we had to move out for the best part of a week as we had no heating or hot water at all. Heating we could deal with (beg, steal, borrow) but our only shower is a mixer. Worth considering whether that matters to you but she didn't want to lose the backup which she would have with the combi.

Good point.

It also connects with combi owners making a panic purchase when it fails in winter, paying peak prices to whoever happens to be available.

though you can get by with an electric shower, which is quite weedy but adequate to tide you over.

There's no back up, an electrician mentioned adding some sort of emergency heating element but the plumber looked at the tank and said it would be possible because of how it's sealed. I've come to the conclusion we should get it replaced asap and leave some 'tails' or whatever the proper name is for points to add on to once the extension is done. Can size everything based on what we will have eventually. Thanks for the advice, very helpful!

Typo - wouldn't be possible to add emergency backup

"plumber looked at the tank and said it would be possible because of how it's sealed"

Do you mean the cylinder?

What colour is it?

post a pic please

BTW you mention replacing pipes.

If they are copper (check them with a magnet because there were some short-lived copper-plated steel ones) they won't need replacing, and if they have soldered joints they're not likely to leak. Old steel radiators, however, may be corroded and need replacing.

It's normal to clean out the system, most often by powerflushing but a chemical clean plus filter may do, of old open-vented systems.

Or are your pipes microbore (the size of a pencil)?