Worth getting a new boiler?

pensionpawn

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.

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?

If it was 65% in 1989 I'll be amazed if it's half that now. I would put money on a new boiler using a third of the gas you're presently using. I replaced my 26 year old boiler at the end of September. I'm still tweaking around with the boiler flow setting and the Nest controller and coupled with a warmer than average autumn and a change to domestic habits it's difficult to determine the impact of just the new boiler. That said I'm presently at 2/3's of my usage this time last year. It will be Dec - Feb that I really see the impact. My Viessmann cost £3k6 installed and so far so good. Pay back (which a year or two ago wasn't even a consideration), approx 5 years. 

doodling

Hi,

Astria said:

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.

I'm not sure that the advice I've bolded above makes sense.  Turning off radiators will mean that the boiler needs to burn less gas because it won't need to do as much heating.  Yes, it is possible that that will cause the return temperature to rise and thus reduce efficiency but I can't conceive of a circumstance where that would offset the reduction in consumption due to not heating that room.

What is the basis for your suggestion that cost might increase?

BUFF

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.

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

How modern? Afaik pre-V3 are a Class I thermostat (pretty basic/not the best), V3 is a Class IV.

doodling said:

Hi,

Astria said:

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.

I'm not sure that the advice I've bolded above makes sense.  Turning off radiators will mean that the boiler needs to burn less gas because it won't need to do as much heating.  Yes, it is possible that that will cause the return temperature to rise and thus reduce efficiency but I can't conceive of a circumstance where that would offset the reduction in consumption due to not heating that room.

What is the basis for your suggestion that cost might increase?

Iirc it can cause short cycling.

victor2

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.

The pilot light on our old Ideal Mexico boiler (circa 1990) used 4.6kWh of gas a day (1679kWh/year).

We replaced it for a combi last year and had our hot water tank removed at the same time, as we hardly used it, having an electric shower. Not because the boiler died on us but more because we'd had over 5 years of the boiler service engineer saying "it's on its last legs you know" accompanied by a sharp intake of breath!

The new one has a programmable thermostat and most radiators have TRVs on them. The heating is now better controlled, more comfortable, and our gas annual usage has dropped by about 35%. We're planning on changing the electric shower to one driven off the combi next year, so gas usage will increase a bit, although electricity usage should fall by a greater monetary value.

Only drawback we've noticed with the combi is the length of time it takes hot water to get through to the kitchen tap, as the water goes upstairs through the (cold) pipework to where the tank was, then downstairs again to the kitchen.

The installation involved the system being flushed and the new boiler has a 10 year warranty, so while we don't expect to get the same lifespan as the old one, we're optimistic that we'll get at least 10 years.

macman

You may well need the gas supply upgrading from the meter to the boiler if you switch to a combi, to satisfy the hot water on demand side, which needs maybe 3-4 times the CH heat demand.

doodling

Hi,

BUFF said:

doodling said:

Hi,

Astria said:

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.

I'm not sure that the advice I've bolded above makes sense.  Turning off radiators will mean that the boiler needs to burn less gas because it won't need to do as much heating.  Yes, it is possible that that will cause the return temperature to rise and thus reduce efficiency but I can't conceive of a circumstance where that would offset the reduction in consumption due to not heating that room.

What is the basis for your suggestion that cost might increase?

Iirc it can cause short cycling.

But that isn't really much of an issue in a boiler that age.  All it will do is lead to a bit more wear of the gas valve which is probably built like a brick outhouse anyway (and can probably be cheaply replaced).

What would be a problem is reducing the flow through the boiler to a level where the temperature rises so quickly when the burner kicks in that it overheats potentially causing damage before the thermostat can turn off the burner - if you're getting that problem then you need to look at why the flow rate is so low. Normally the culprit is fitting thermostatic valves to all radiators rather than leaving one radiator unfitted with an open valve on each end.

BUFF

doodling said:

Hi,

BUFF said:

doodling said:

Hi,

Astria said:

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.

I'm not sure that the advice I've bolded above makes sense.  Turning off radiators will mean that the boiler needs to burn less gas because it won't need to do as much heating.  Yes, it is possible that that will cause the return temperature to rise and thus reduce efficiency but I can't conceive of a circumstance where that would offset the reduction in consumption due to not heating that room.

What is the basis for your suggestion that cost might increase?

Iirc it can cause short cycling.

But that isn't really much of an issue in a boiler that age.  

It won't run at the same efficiency though as a constant low flow (it was specific to a condensing boiler). The difference is probably minimal though.

kittennose

pensionpawn said:

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.

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?

If it was 65% in 1989 I'll be amazed if it's half that now. I would put money on a new boiler using a third of the gas you're presently using. I replaced my 26 year old boiler at the end of September. I'm still tweaking around with the boiler flow setting and the Nest controller and coupled with a warmer than average autumn and a change to domestic habits it's difficult to determine the impact of just the new boiler. That said I'm presently at 2/3's of my usage this time last year. It will be Dec - Feb that I really see the impact. My Viessmann cost £3k6 installed and so far so good. Pay back (which a year or two ago wasn't even a consideration), approx 5 years. 

So you're saving 33% on last year's usage? That's pretty good.

Astria

doodling said:

Hi,

BUFF said:

doodling said:

Hi,

Astria said:

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.

I'm not sure that the advice I've bolded above makes sense.  Turning off radiators will mean that the boiler needs to burn less gas because it won't need to do as much heating.  Yes, it is possible that that will cause the return temperature to rise and thus reduce efficiency but I can't conceive of a circumstance where that would offset the reduction in consumption due to not heating that room.

What is the basis for your suggestion that cost might increase?

Iirc it can cause short cycling.

But that isn't really much of an issue in a boiler that age.  All it will do is lead to a bit more wear of the gas valve which is probably built like a brick outhouse anyway (and can probably be cheaply replaced).

What would be a problem is reducing the flow through the boiler to a level where the temperature rises so quickly when the burner kicks in that it overheats potentially causing damage before the thermostat can turn off the burner - if you're getting that problem then you need to look at why the flow rate is so low. Normally the culprit is fitting thermostatic valves to all radiators rather than leaving one radiator unfitted with an open valve on each end.

You also need to look at the overall heat loss of the property. Typically you heat a house not a room and so internal walls are typically more for dividing than containing heat. A cold room will therefore cause heat loss in adjacent rooms to be higher (both to the side and below) and thus will require more heat, so the radiators in those room will need to do more work. Depending on where the thermostat is could then mean that it calls for heat more often or for longer periods depending on the sizing of those radiators.

The end result is that shutting off a room might not actually save you any energy whatsoever, and combined with other factors, may actually increase energy usage.

FreeBear

doodling said:

Hi,

BUFF said:

doodling said:

Hi,

Astria said:

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.

I'm not sure that the advice I've bolded above makes sense.  Turning off radiators will mean that the boiler needs to burn less gas because it won't need to do as much heating.  Yes, it is possible that that will cause the return temperature to rise and thus reduce efficiency but I can't conceive of a circumstance where that would offset the reduction in consumption due to not heating that room.

What is the basis for your suggestion that cost might increase?

Iirc it can cause short cycling.

But that isn't really much of an issue in a boiler that age.  All it will do is lead to a bit more wear of the gas valve which is probably built like a brick outhouse anyway (and can probably be cheaply replaced).

What would be a problem is reducing the flow through the boiler to a level where the temperature rises so quickly when the burner kicks in that it overheats potentially causing damage before the thermostat can turn off the burner - if you're getting that problem then you need to look at why the flow rate is so low. Normally the culprit is fitting thermostatic valves to all radiators rather than leaving one radiator unfitted with an open valve on each end.

There should be a thermostat inside the boiler to shut down the gas if it detects an excessive rise in temperature of the water - My vintage Baxi back boiler has such a device..