Worth getting a new boiler?

kittennose

I am trying to crunch some numbers to see if it is worth replacing our ageing, but working, boiler.

Current boiler: GlowWorm Space Saver MKII (1989) - 65% efficiency (when new).
Replacement: Combi - 90% efficiancy
Efficiency Saving: 25% 
Current annual gas usage / cost: 20,000kWh (£2,000)
Replacement Cost: £3800
Annual Saving: £500 per year

Despite our boiler being vintage, it would appear it's going to take 8 years to make money back; by which time any new boiler could be on it's last legs.

However there are elements I cannot calculate such as a chance that our old boiler is far less efficient than 65% when new. Sludge in radiators, age of boiler and the fact  we live in a hard water area will mean it's full of limescale. We also have the hot water tank on for 45 mins each day and sometimes don't use it all. With a combi we would only heat what we need.

Thoughts?

Astria

I'm waiting to see what happens when they attempt to ban gas boilers in 2025 and any new advancements in heat pump technology.

Don't use the hot water tank at all and use instant hot water - yes it's less efficient, but for the amount we use its actually cheaper than heating up a big tank, so the tank is heated at most once a week - when we predict we'll be using a lot of hot water.

[Deleted User]

kittennose said:

We also have the hot water tank on for 45 mins each day and sometimes don't use it all. With a combi we would only heat what we need.

With a heat pump you would need a hot water tank

[Deleted User]

Sadly, it is not as simple as suggesting that a 25% difference in boiler efficiency will result in 25% lower energy bills. Most modern condensing boilers are not run in an efficient mode. The efficiency improvement comes from a boiler return temperature of less than 56C. The lower the return temperature the greater the boiler efficiency as more heat can be extracted from the exhaust gas flow.

When heating hot water, a combi boiler is anything but efficient. I have a 250l unvented cylinder which I heat via my immersion heater rather than gas. Yesterday, it took 3kWh of electricity to re-heat the cylinder to 60C. If I used gas it would more than 6kWh because of boiler efficiency and pipe losses.

I am currently running my 24kW system boiler at 55C flow temperature. Yes, it takes longer in the mornings for my home to reach its set temperature but, so far, my total usage today has been 15.69kWh. Clearly, the return flow temperature is well below the 56C threshold.

FWiW, my advice is do not put a new boiler onto an old heating system without having the system professionally cleaned. Sludge is a known killer of new condensing boilers and it is excluded from all warranty claims.

Finally, if you can, choose a boiler with Opentherm Control. OT Control is now mandated in many European countries. 

macman

Astria said:

I'm waiting to see what happens when they attempt to ban gas boilers in 2025 and any new advancements in heat pump technology.

Don't use the hot water tank at all and use instant hot water - yes it's less efficient, but for the amount we use its actually cheaper than heating up a big tank, so the tank is heated at most once a week - when we predict we'll be using a lot of hot water.

The proposal is to ban gas boilers in new-build properties-there will still be millions of new boilers installed as replacements in existing properties, and working for decades thereafter.
OP: the one factor you haven't taken into account is what you might have to spend in repairs in the next 8 years keeping your old boiler working? And the fact that your gas bills could rise another 50% next spring?
I wouldn't rush into switching to a combi though. The heat 'wasted' in heating a hot tank of water serves to heat the property in winter, so it's not really wasted, and heat loss from a properly insulated tank is minimal. You also need to assess if the water pressure and gas supply are even suitable for a combi?
A new boiler won't be on it's 'last legs' at 8 years. Decent brands (Viessmann, Vaillant etc) come with an 8 or even 12 year warranty now.
Finally, £3.8k estimate for a new boiler seems excessive-does that include other work on the CH as well?

FreeBear

Does this GlowWorm have a pilot light permanently on ?

I suspect it does, in which case, you could be wasting some 2500KWh (or more) per year. Factor that cost in to your potential savings, and I think you'll find the payback period drops quite a bit.

BUFF

kittennose said:

I am trying to crunch some numbers to see if it is worth replacing our ageing, but working, boiler.

Current boiler: GlowWorm Space Saver MKII (1989) - 65% efficiency (when new).
Replacement: Combi - 90% efficiancy
Efficiency Saving: 25% 
Current annual gas usage / cost: 20,000kWh (£2,000)
Replacement Cost: £3800
Annual Saving: £500 per year

Despite our boiler being vintage, it would appear it's going to take 8 years to make money back; by which time any new boiler could be on it's last legs.

If your controls are of similar vintage I would suggest that updated & more efficient modern controls (programmer/room 'stat/TRVs) & the increased control that you will have via them along with a new, properly set up condensing boiler could see a higher % saving (especially if, as already mentioned; your existing boiler has a permanent pilot). It could even be up to~50% (personal experience).

& your existing boiler might fail tomorrow ... 

macman said:

Astria said:

I'm waiting to see what happens when they attempt to ban gas boilers in 2025 and any new advancements in heat pump technology.

Don't use the hot water tank at all and use instant hot water - yes it's less efficient, but for the amount we use its actually cheaper than heating up a big tank, so the tank is heated at most once a week - when we predict we'll be using a lot of hot water.

The proposal is to ban gas boilers in new-build properties-there will still be millions of new boilers installed as replacements in existing properties, and working for decades thereafter.
OP: the one factor you haven't taken into account is what you might have to spend in repairs in the next 8 years keeping your old boiler working? And the fact that your gas bills could rise another 50% next spring?
I wouldn't rush into switching to a combi though. The heat 'wasted' in heating a hot tank of water serves to heat the property in winter, so it's not really wasted, and heat loss from a properly insulated tank is minimal. You also need to assess if the water pressure and gas supply are even suitable for a combi?

The Scottish govt. are proposing banning replacement installs from 2025 as well.
I agree that switching to a combi should be a considered decision -especially as the next replacement cycle will almost certainly require stored hot water.


Vaillant, Viessmann & Worcester all have their own equivalent communications protocols to OpenTherm (in fact there is some evidence to show that they may be marginally better) but theirs are proprietary & for best efficiency you would want to use their own controls.

kittennose

macman said:

Astria said:

I'm waiting to see what happens when they attempt to ban gas boilers in 2025 and any new advancements in heat pump technology.

Don't use the hot water tank at all and use instant hot water - yes it's less efficient, but for the amount we use its actually cheaper than heating up a big tank, so the tank is heated at most once a week - when we predict we'll be using a lot of hot water.

The proposal is to ban gas boilers in new-build properties-there will still be millions of new boilers installed as replacements in existing properties, and working for decades thereafter.
OP: the one factor you haven't taken into account is what you might have to spend in repairs in the next 8 years keeping your old boiler working? And the fact that your gas bills could rise another 50% next spring?
I wouldn't rush into switching to a combi though. The heat 'wasted' in heating a hot tank of water serves to heat the property in winter, so it's not really wasted, and heat loss from a properly insulated tank is minimal. You also need to assess if the water pressure and gas supply are even suitable for a combi?
A new boiler won't be on it's 'last legs' at 8 years. Decent brands (Viessmann, Vaillant etc) come with an 8 or even 12 year warranty now.
Finally, £3.8k estimate for a new boiler seems excessive-does that include other work on the CH as well?

Had 4 quotes, all between £3600 - £4000. + British Gas who were nearer £6k!!! These are from Box, PrimeTime Boilers, Heatable and a local fitter.

Water pressure is fine and I assume gas supply.

kittennose

FreeBear said:

Does this GlowWorm have a pilot light permanently on ?

I suspect it does, in which case, you could be wasting some 2500KWh (or more) per year. Factor that cost in to your potential savings, and I think you'll find the payback period drops quite a bit.

Yes it does, always on. 2500kWh for that?! Crickey. That's £250.

PS: We have modern Hive controls but no radiator TRVs. We just turn off the ones we don't use.

Maybe we should consider a standard boiler. The attraction to a combi was instant hot water, better shower pressure, plus the additional storage boost in the attic and airing cupboard. No other reason.

[Deleted User]

kittennose said:

FreeBear said:

Does this GlowWorm have a pilot light permanently on ?

I suspect it does, in which case, you could be wasting some 2500KWh (or more) per year. Factor that cost in to your potential savings, and I think you'll find the payback period drops quite a bit.

Yes it does, always on. 2500kWh for that?! Crickey. That's £250.

PS: We have modern Hive controls but no radiator TRVs. We just turn off the ones we don't use.

Maybe we should consider a standard boiler. The attraction to a combi was instant hot water, better shower pressure, plus the additional storage boost in the attic and airing cupboard. No other reason.

Don't you have instant hot water by having a tank full of it ready to go?

And for shower pressure and storage boost (in the attic) - consider a system boiler and unvented cylinder.  Might be more expensive to buy overall (although the boiler will likely be cheaper) but could give you some of the benefits you want if one would work in your situation.

Astria

kittennose said:

FreeBear said:

Does this GlowWorm have a pilot light permanently on ?

I suspect it does, in which case, you could be wasting some 2500KWh (or more) per year. Factor that cost in to your potential savings, and I think you'll find the payback period drops quite a bit.

Yes it does, always on. 2500kWh for that?! Crickey. That's £250.

PS: We have modern Hive controls but no radiator TRVs. We just turn off the ones we don't use.

Maybe we should consider a standard boiler. The attraction to a combi was instant hot water, better shower pressure, plus the additional storage boost in the attic and airing cupboard. No other reason.

If your boiler is non-condensing then turning off the radiators you don't use is fine, but you should still allow adequate ventilation in those rooms to prevent things like damp (ie, don't close them off completely)

If your boiler is condensing then you should refrain from turning off radiators as it could actually make your boiler less efficient and so, in some cases, actually cost more.

But you should however ensure that your radiators are correctly balanced.