If replacing a boiler, what would you fit?

[MisterBoy]

We have a Baxi Duo-tec combi 40 HE A, to my knowledge it's about 10 years old and for the last 3 has been plagued by problems... Just this week it has started leaking a couple of litres a day from the leftmost pipe underneath and needs pressurising daily, only 6 months after the last thing broke. Think that'll be the 5 or 6th time we've had to have it fixed on top of regular servicing.

As far as I understand, 40kW is pretty big and it probably needs to be as we have an old solid brick detached Victorian house. We've been talking about replacing it for a while and it seems we're just throwing good money after bad now.

We don't use a huge amount of hot water through the day, except that I have a big deep bath that I like piping hot most evenings.

After fitting them was all the craze 15 years ago I understand combis are out of fashion now? And also that in a few years gas boilers night be outlawed(!?)
So what would you install in its place? Is there a single obvious answer or are there lots of options - how do I decide? Obviously I talk to my plumber as well.

Thanks

 

[delmel]

so far as I understand pretty much all modern boilers are crap. 10 year life span is considered good. Worst thing i did was have a new boiler 7 years ago. You ask 3 differnet installers, you will likely get 3 different answers. They will likely recommend ehat they install or are familiar with, it doesnt mean they are the best. I am unsure what the best are in the modern day.

 

[flameport]

40kW will be grossly oversized for the heating load.
It may be oversized for the hot water as well, but that depends on the water pressure/flow and how much hot water you actually require.

After fitting them was all the craze 15 years ago

Combis are 1970s technology. They are preferred by many as they are cheap to install and don't require space for a hot water cylinder which may be a benefit in a tiny property.

And also that in a few years gas boilers night be outlawed(!?)

Very likely.

If you want a new gas boiler now, get one that's cheap and has a long warranty.

 

[MisterBoy]

40kW will be grossly oversized for the heating load.
It may be oversized for the hot water as well, but that depends on the water pressure/flow and how much hot water you actually require.

without knowing I imagine they might have gone for the biggest they could get, although this is not a typical house. 12 rooms, something like 16 rads in a solid brick, mostly single-glazed detached property - the previous owners seemed to have the heating on in every room and were spending £3k on gas a month back in 2017! But I have not even a rough idea what might be a sensible size

Combis are 1970s technology. They are preferred by many as they are cheap to install and don't require space for a hot water cylinder which may be a benefit in a tiny property.

And now it seems they're being replaced en masse with modern tank systems? But these seem quite different from the old type. So my question is more what style of boiler to get? We have already been advised against a combi by virtually everyone. Initially I liked the idea of water on demand but is a tanked system actually more efficient?
I suppose a tank means you can theoretically have more options - such as integrating solar, and in the event the boiler breaks you can in an emergency use an immersion heater to at least have some hot water.

 

[bernardgreen]

This is a very old document but ( in my opinion ) is still valid

http://www.thnet.co.uk/thnet/BF/BFPages/overhist.htm

 

[Dereekoo]

And I keep thinking of changing my 25 year old Ideal Classic FF250 for a combi?? mmmmm!!

 

[SandyLyon]

without knowing I imagine they might have gone for the biggest they could get, although this is not a typical house. 12 rooms, something like 16 rads in a solid brick, mostly single-glazed detached property - the previous owners seemed to have the heating on in every room and were spending £3k on gas a month back in 2017! But I have not even a rough idea what might be a sensible size .

Firstly I’d be looking at how to make the house more efficient, insulation, double glazing etc, this in turn would lower the output of the required boiler.

 

[MisterBoy]

And I keep thinking of changing my 25 year old Ideal Classic FF250 for a combi?? mmmmm!!

I keep seeing ads for modern back boilers on FB of late actually. Not sure if it's targeting all those who ripped out their ancient BB for a combi.

Space for a tank is not something we're short of, although it does raise the question of where the boiler (and tank) can/should go. Pre-gas our house we had a coal-burning boiler in an outhouse but now the combi is fitted in the converted loft space, 20-25 feet up, though ironically the gas meter is on the outhouse the old boiler lived. And then this means when you turn on the hot tap in the kitchen, you've got to run the hot water through 25+ feet of copper pipe which seems wasteful.

 

[MisterBoy]

Firstly I’d be looking at how to make the house more efficient, insulation, double glazing etc, this in turn would lower the output of the required boiler.

We are doing this as rooms come up for decoration but having done the sums, this is a very long-term cost-saving measure.

In any case, it doesn't help the fact we have a dodgy boiler now and aren't going to replace all our windows, etc, in the next year. It seems to need replacing so the question is what with.

 

[vulcancontinental]

Building Research Establishment did a comparison years ago which found system boilers slightly more efficient than combination boilers as a standalone appliance but the losses between the boiler and cylinder negated the advantage, sometimes swaying it in the other direction.

40kW is high output needed only for hot water but if you're happy with that then that's what you need. To confirm measure the flow rate through the hot tap you'll get around 16l/min with a 35 degree rise in temp from cold or a higher rise with less flow if your cold water isn't up to that flow rate.

If you get a combi, if that's what you're going for, get one with a decent modulation, above 1:7 although others put more store by higher ratios than I do. 40kW for heating is completely unnecessary domestically a four bed Victorian house would rarely need more than 20 and probably quite a bit less.

If you're concerned about the future heating configurations get a boiler that can be incorporated or control a hybrid system containing a heat pump or solar whether it be combi or system.

Anything you buy will be hydrogen blend ready and a relatively easy swap to neat hydrogen if you think things will go that way.

All the above is valid however if it were my house I'd simply put a combi in, OpenTherm, Weather comp with setback, maybe modbus for integration with a heat pump or solar. with a long warranty, second guessing the future is often a waste of time.

 

[Agile]

If I were faced with that problem and taking into account unknown fuel shortages which could occur at virtually no notice if Putin targeted our North Sea gas installations, I would fit a small system boiler and a cylinder.

A cylinder can be heated by a gas boiler, mains supplied electricity, solar PV panels or a heat pump. So that would be a good decision for me with totally unknown future energy problems.

I already have solar PV panels so feel somewhat independent of potential supply problems.

Heat pumps are not very "green" until we make all our electricity from nuclear or other green sources. Wind does not blow all the time and the sun does not shine very much either during the winter. We have not invested in water transfer energy storage. The Government seems to not understand what they do.

 

[MisterBoy]

I would fit a small system boiler and a cylinder.

A cylinder can be heated by a gas boiler, mains supplied electricity, solar PV panels or a heat pump. So that would be a good decision for me with totally unknown future energy problems.

Forgive my ignorance but is a system boiler a specific type of boiler, or simply "not a combi?" - i.e. an old back-boiler and a modern tanked system are both using "system boilers?"

I do like the idea of being flexible/backed up and open to PV down the line but while my hot water cylinder can be heated by any means, presumably my heating would still be reliant on the gas boiler as normal. As @vulcancontinental says, trying to get too elaborate and second-guess the future is probably going to be complicated and expensive.

 

[Agile]

A "system boiler" is a maker's marketing tool I think, where they offered a boiler with virtually everything you need built inside it so all you need to do is pipe up some rads to it. Probably first heard of about 20 years ago when a combi had become most installer's solution.

The idea is that it cuts down installation time on site and makes that type of boiler desirable. Because the manufacturer buys bits like pumps in huge bulk quantities the overall cost can be cheaper too. It also enables the design to have better control facilities built in.

Some manufacturers have taken the initiative further and make "four pipe" boilers with diverter valves inside to be used with radiator and cylinder installations.

 

[gas112]

a 40kw duotec output is for hot water it only gives out 32 ish for heating the duotec is usually a solid boiler and absolute doddle to repair sounds like someone is struggling with the basics on how to repair it.