Worth getting a new boiler?

doodling

Hi,

Astria said:

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.

Can you give me a worked example of how that increased energy use would happen?

I don't believe that heating less will cost more.  It is both counterintuitive at a basic level and at my level of understanding of gas central heating systems.

I would certainly agree that there may be other factors at a whole house level which might result in additional cost if you turned off the heating in some rooms (e.g. in the event that there was insufficient extraction of moist air at sources like showers and cooking which lead to damaging damp in the unheated rooms) but those don't lead to an energy cost increase which is what you were suggesting.

doodling

Hi,

FreeBear said:

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..

All boilers will have such a thermostat (of varying levels of complexity) as otherwise the boiler would keep heating the water until it turned to steam if there will still a heat demand from the room thermostat.

They may not be fast enough acting to provide protection against damage in the case where there is no flow through (or, in the worst case, no water in) the boiler as the temperature will rise very quickly.

Having said that, a boiler of that age will probably have a cast iron heat exchanger which will withstand a brief overtemperature in the no flow case - a more modern boiler with an alloy heat exchanger might not be so forgiving however (which is why modern boilers often have flow switches (in the CH circuit) as well as thermostats to make sure that the heat exchanger is protected).

mksysb

I woudn't touch a combi, when it goes wrong you'll have no hot water.  At least with a hot water tank, you'll have an immersion heater to use in an emergency.

Astria

doodling said:

Hi,

Astria said:

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.

Can you give me a worked example of how that increased energy use would happen?

I don't believe that heating less will cost more.  It is both counterintuitive at a basic level and at my level of understanding of gas central heating systems.

I would certainly agree that there may be other factors at a whole house level which might result in additional cost if you turned off the heating in some rooms (e.g. in the event that there was insufficient extraction of moist air at sources like showers and cooking which lead to damaging damp in the unheated rooms) but those don't lead to an energy cost increase which is what you were suggesting.

Can't really give a worked example as there really are too many variables, just make sure you know how much you are paying before and after making alternations to your home heating system so you can see what works for you than assuming. The main problem is the human - if someone feels cooler you are more likely to change the thermostat and higher heat loss can make someone feel cooler.

I did come across one property where all the downstairs were active and where the thermostat was and all the upstairs radiators were turned off because "We prefer the bedrooms cooler, and they still keep at 15c even with the radiators off", the boiler was less efficient because the return water temperature was higher, shut down earlier because the temperature was too high (short cycling), so basically it was heating downstairs more since the changes (because heat rises and there was only floorboards and carpet between the rooms).  They had increased thermostat because they felt cool. I told them to turn the radiators upstairs back on at a low flow and they didn't notice any increase in their gas bills.

pensionpawn

kittennose said:

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.

Yes, that's good however I'm not sure how much of that saving is presently due to the weather. Time will tell.

Snookie12cat

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.

@Astria Can you elaborate further on this? I have a system boiler but have turned two of the rads off - is this not a good idea?

Astria

Snookie12cat said:

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.

@Astria Can you elaborate further on this? I have a system boiler but have turned two of the rads off - is this not a good idea?

Where are the rooms located? If for example the thermostat is in the lounge, and the room above the lounge is unheated, the lounge will lose heat faster into that room, so your thermostat will trigger more often to keep the lounge warm, so keeping those other rooms warmer will keep the lounge warmer too, which could make you feel more comfortable at a lower thermostat temperature and thus may reduce your bill.

Central heating systems are tricky, you should always check how much it's using before and after making changes to it, it gets even more confusing when you start introducing heat pumps into the mix and your radiators are then ~40c instead of ~60c.

Alnat1

mksysb said:

I woudn't touch a combi, when it goes wrong you'll have no hot water.  At least with a hot water tank, you'll have an immersion heater to use in an emergency.

You would if the person who fitted the tank wired up the immersion. The previous occupier of our house runs a plumbing and heating business and didn't get his own immersion wired. We've been told his dad was a sparky.........It's something we've been meaning to get sorted -for the last 3 years 

Astria

Alnat1 said:

mksysb said:

I woudn't touch a combi, when it goes wrong you'll have no hot water.  At least with a hot water tank, you'll have an immersion heater to use in an emergency.

You would if the person who fitted the tank wired up the immersion. The previous occupier of our house runs a plumbing and heating business and didn't get his own immersion wired. We've been told his dad was a sparky.........It's something we've been meaning to get sorted -for the last 3 years 

When we moved into our current house we discovered the previous occupant was a bit of a DIYer, found out that whenever the heating was on the hot water was also on because it was wired incorrectly, which also meant that the pump was always on during the time periods of heating regardless of thermostat or cylinder stat. No wonder he said that he'd recently changed the main pump!

Alnat1

Bet you haven't got a cold only shower over your bath, but a hot and cold tap outside though?