Time to upgrade to a "modern" (Combi) Boiler?

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Hi all,

Not sure if this is the right place to ask, and I'm sure the answer will depends on my property etc...

So I live in a 40 yrs old detached property, with 4 bedrooms, 2 bathrooms. We have a Baxi boiler which I'm sure came with the property, uses water tank in the loft and a hot water cylinder. The odd thing about the CH system is that it doesn't conform to any "plans". It only has 1 valve... so it's either HW and CH on or off together. I can't control them individually. So every summer I have to turn all the radiators off to save on central heating bill.

Despite that my gas bill seems to be rather high. Our annual usage for gas is nearly 30000 kWh. Note that I "only" keep the temp around 21C during the winter when we ar at home. so about ~6hrs in the weekdays and ~9 hours at the weekend. We have gas hobs, and don't use our gas fire that much if at all.

With the recent and impending rise in cost of energy, and British Gas (amongst others) advertising interest free boiler installation, I wonder whether it is the time to upgrade. I am hoping a combi boiler will be more efficient, and therefore reduce my gas bill. The boiler hasn't given me any problem in the 11 years we've lived here. It needed some new parts at the last service which didn't exactly cost an arm or a leg. I'm hoping to break even in terms of cost after 3 to 5 years-ish.

Any advice welcomed. Thanks all.
 
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At 30,000kwh p/a that's £1000 p/a on gas in round numbers. You've not said what boiler you have (Baxi have made a lot of different boilers) but if we assume you have an efficiency Band F boiler and you go for a full maximum energy efficency upgrade of a good quality boiler correctly sized for your house, good quality TRVs on every radiator, a smart load compensating controller and everything balanced & set up correctly you might be able to achieve a 30% saving on your bills. For something like that you'll be paying out in the region of £5000, giving you a payback of about 17 years. If you go for a BG install you'll maybe get it for a bit less but they'll do minimal setup of the boiler and system, sell you cheap TRVs and probably a Hive, which is a cheap nasty on/off thermostat with an Internet connection. Say they charge you £4k but you only achieve 20% energy saving. Payback is now 20 years.

Either way, your goal of getting a payback in 3-5 years is highly unrealistic. It's just not going to happen - the maths just don't work. If you want a cheaper way of improving your energy bills, improve your loft insulation, turn down your thermostat (mine is set at 17...) and invest in a pullover.
 
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I am hoping a combi boiler will be more efficient,

A heat only boiler or a system boiler could be a better option for you than a combi. The power rating of a combi has to be large enough to provide instant hot water. Even though most boilers can modulate ( reduce ) the amount of heat they generate this reduced power may still be too high for just keeping the house warm. The boiler then has to cycle ON and OFF which is both inefficient use of gas and increases wear and tear on the boiler.
 
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It only has 1 valve... so it's either HW and CH on or off together. I can't control them individually. So every summer I have to turn all the radiators off to save on central heating bill.
That situation can be improved significantly for a fraction of the cost of a new boiler.
 
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Stick with a heat only boiler; are you confusing 'combi' with 'condensing'? Many do.
All modern boilers are the condensing type, using around 15% less gas for the same heat output.
Upgrading controls and pump will save a bit more gas and electricity.
Suggest you keep your hot water cylinder; it will pay benefits if you come to install solar pv panels.
Insulate, insulate, then insulate more. Keep the heat in and the bills down.
All this is somewhat reinforcing others' comments.
 

DP

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Either way, your goal of getting a payback in 3-5 years is highly unrealistic. It's just not going to happen - the maths just don't work. If you want a cheaper way of improving your energy bills, improve your loft insulation, turn down your thermostat (mine is set at 17...) and invest in a pullover.

Not forgetting the maintenance and cost of parts plus the fickle nature of modern condensing boilers. Then there is limited lifespan of approx 10 years.
Forget the new boiler, insulate the house and fit better controls eg Evohome
 

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The odd thing about the CH system is that it doesn't conform to any "plans".

Instal a motorised valve and thermostat on the cylinder
You will then be able to control Heating and hot water from a timer and thermostat
 
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Not forgetting the maintenance and cost of parts plus the fickle nature of modern condensing boilers. Then there is limited lifespan of approx 10 years.
Forget the new boiler, insulate the house and fit better controls eg Evohome
The 10 year lifespan thing is a total myth put about by box slingers. No reason why they shouldn't last twice that long if properly installed and maintained
 
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The 10 year lifespan thing is a total myth put about by box slingers. No reason why they shouldn't last twice that long if properly installed and maintained
I serviced a boiler that I fitted 15 years ago yesterday, had a 7 year warranty, serviced every year by myself and it looks like it has just been taken out of the box, customer kept saying should she replace because she had read the 10 year crap, perfectly good boiler, ignore boiler slingers
 

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The 10 year lifespan thing is a total myth put about by box slingers. No reason why they shouldn't last twice that long if properly installed and maintained


I serviced a boiler that I fitted 15 years ago yesterday, had a 7 year warranty, serviced every year by myself and it looks like it has just been taken out of the box, customer kept saying should she replace because she had read the 10 year crap, perfectly good boiler, ignore boiler slingers

I too service condensing boilers that are easily 15 years old. Examples are ideal icos, Isar, vokeras to name three. Similarly have removed others that are not yet 10 years old ( Alpha, Ariston, Glow worm that was much older though) and that is me being mostly a repairer and sometimes a boiler changer. Yet have boiler that are at times older than 30 years ( Flowmatic, Potterton Netaheat etc).

Here are some examples
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1D55DA1E-8436-4949-9B62-366BDE6C7372.jpeg
D16F3433-0782-47F8-9D1B-B580E2441466.jpeg
B59DC143-5F24-4AAF-A32F-9C0967778AA3.jpeg
B0C43859-A1D7-46BF-9EFD-BEA4249476C5.jpeg
 
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My old house when built had no central heating around 1978, it had a single 4.5 kW gas fire in living room, and open plan so that would heat whole house.

However problem with gas fire no auto regulation of heat output, so central heating fitted, standard system for the time, header tanks, cylinder and a hot coil fitted in the cylinder to heat domestic hot water, but we wanted the room used by the cylinder to convert it into a bedroom so cylinder removed and a second gas boiler fitted (Main 7) that supplied domestic hot water direct.

Neither boilers used the latent heat, so both rather basic. The DHW worked well, but needed a large shower rose, as if not enough water used the boiler would cut off. It also resulted in cold water pressure to hot water, but original pipes used so around 2 pints extra used every time we wanted hot water as boiler warmed up, smaller diameter pipes could have reduced this, but I had no intention to renew them.

Father-in-law two doors up same design of house, but not removed cylinder was able to have solar water heating, it did not work, but he could have done, he could also have an immersion heater in the summer, since our cylinder removed we did not have option. We both had hot water in an electric power cut, but his would run out, ours would not. His was S plan so central heating still heated DHW.

Our bill dropped when we moved here and went to oil central heating, and our son took over our old house, there was a leak in one of the old boilers, so both swapped for a modern combi boiler, it made no real change to operation, except now no electric means no hot water, and he can work with a lower flow rate and still get DHW. However the bills actually went up.

All theory says his bills should have dropped, but that has not happened. Not a clue why, maybe they keep the house warmer, or have more baths, but his bill is double ours for oil, OK oil boiler 4 times price of gas boiler, so swapping to oil not an option, but the new combi is more expensive to run to old independent boilers.

The house had no TRV's fitted down stairs, but were fitted up stairs, mainly to stop upstairs getting too hot, and one reason why the combi may not be working well is the lack of TRV control. The Myson fan assisted radiator has no restriction to water flow, again this may be causing problems with return water too hot. Not my worry any more, he can fit the TRV's, however if the lack of TRV's is the problem, then clearly as part of the upgrade you need to add all TRV control and if not in the boiler a by-pass valve.

So
That situation can be improved significantly for a fraction of the cost of a new boiler.
is very true, and it would seem prudent to fit TRV heads first, as will be needed if boiler changed.

Stick with a heat only boiler; are you confusing 'combi' with 'condensing'? Many do.
All modern boilers are the condensing type, using around 15% less gas for the same heat output.
Yes all modern boilers are condensing type, but to use the latent heat, the controls must match, so one all radiators need to be larger as running cooler, also if using programmable TRV heads you need to be able to use the boilers minimum output with the main rooms, you want boiler to modulate not cycle.

The whole control concept changes, the TRV is king, the modern boiler can have three controls, return water temperature, on/off electric, or up/down electric, the on/off electric control results in any heat in boiler going out of flue each time it turns off, and when it switches back on, it does so flat out, so on/off control should be kept to a minimum.

If the control does not match the boiler, for example a wall thermostat which uses mark/space control to stop over shooting, it can turn the clever condensing type boiler into an old type non condensing, the new boiler should turn up/down not off/on to control output.

With this in mind, to add TRV heads to every radiator the only cost over and above what will be needed with a new boiler is the by-pass valve which is likely included inside new boiler, but you will likely need to install outside old boiler or have one radiator without a TRV head. If the radiator in the room with the wall thermostat is left without a working TRV head then no need for by-pass valve.

15% gain for a £1000 new boiler, with a £500 year fuel bill is around 14 years to pay back, if you include interest on that money then longer, so you need to plan to stay in the house for 20 years with existing boiler to gain, old boilers could last 25 years, new boilers seem not to last as long, so yes when son's boiler started to leak, needed to be changed, but if still working, then move one is better control, which you will need if you change boiler anyway.
 
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It's also not only about money, at 30,000 kwh/annum that's just under double the UK average energy use for domestic heating and hot water. Multiplied by 0.185kg/kwhr CO2 that means you're putting over 5 tonnes of CO2 into the atmosphere so there's something to work with.

I haven't got the figure for NoX here (acid rain and some say more of a contributor to climate change than CO2) but again there's a saving to be made. Look for figures on emissions in boiler booklets and if that is an important issue to you don't look for NoX as a class (they'll all be class 6) look for actual figures. 18 to 23 is very good, class 6 is up to 54mg/kwh.
 
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