When is it worth replacing gas boiler?

[Cynderella]

I'm pretty good at working out where to reduce the electricity I'm using, but I need to tackle gas. We use a lot. In our old house, we used about 30,000kwh a year, so this one is better - 20,000kwh a year.

But, obviously that's a lot - almost twice the average. We are four adults in a 3 bed Victorian mid terrace house. Windows double glazed, curtains, carpets and rugs, so pretty average there. I do cook a lot and there's four showers a day - between 3-10 mins each. Dishwasher, so only one lot of washing up water.

We're averaging 250kwh a month with no heating on. The boiler was installed in 2008 and is a Vailant Ecotec 831 - with 89% efficientcy and maximum output of 25kwh.

I'm resigned to not having the heating on when I want it this winter - we're on a standard variable rate, so not in a position to do anything else. But would it be worth replacing the boiler - has anyone done this just to save money rather than because it was not working properly?

I don’t know but I’d be interested in answers. Our boiler was installed in 2003. Previous boiler was over 20 years old so not sure if ours is getting to the end of it’s life.

The gas won’t be heating up the dishwasher will it? Would an electric shower be a cost saving?

No, dishwasher and washing machine are cold fill. I was just saying we don't use a lot of hot water apart from the showers every day. Quite happy with our shower, and I've now got everyone to limit them to a few mins instead of twenty. I don't imagine an electric shower would work out cheaper? Or, if it did, cheap enough to claw back the cost of buying and installation.

I think the heating's our issue.

Yeah dh was in the shower earlier (electric) and the meter went up to £2.11 an hour! I keep telling everyone to have shorter showers. This will be our first winter with a smart meter so will be interesting to see gas usage once the heating goes on.

How long is the heating on for and what is the thermostat set at? How long is the hot water on for?

Gas is cheaper than electricity so I would stick with your existing showers

I doubt you'll see a significant saving by replacing that boiler, certainly won't recoup the cost in the lifetime of the new one (they don't build them like they used to, despite being a bit more efficient).

That does sound a huge amount of gas usage. 250kWh a month just on showers/hot water? Gas oven/hob shouldn't take much at all compared to the boiler. For comparison I also live in a 3 bed terraced, but it's stone construction (solid walls), and the loft/roofs are really badly insulated - 1970's standard, but can't be upgraded without pulling down the ceilings and rebuilding the flat roof extension. One adult and 3 kids. Just worked out our annual gas consumption as 3250kWh. Yours is 6 times as much!

We have an electric shower, so we use no gas boiler usage for showering. I'm considering replacing the electric shower with one that runs from the combi boiler though, because hot water from gas is cheaper than electric.

Maybe you could turn down your central heating, that's got to be the biggest gas usage? My heating central heating never comes on between mid April and end of October. Barely use any hot water, so gas usage for 6+ months of the year is practically zero. I guess it depends where in the country you are, I'm SW so lucky that we don't get quite as cold weather as up North.

When our old boiler finally packed up in our old house, we had it replaced with a Worcester Bosch boiler and our bill was exactly the same. So for us, I wouldn't replace the boiler as I don't think you'll get much benefit.

Just checked our gas consumption, it was 100kw last month. 2.5 adults (adult DD home only half of time). We've been trying to cut shower time. Also, choosing to cook things that require slightly less cooking time, unless it's a very cheap meal. I've also been switching oven off a couple of minutes early and leaving meal to cook for five mins. It was 148 August 2021 (I give monthly readings) so our efforts have made a difference.

We're also in the south, so don't have the heating on at all in the summer. I probably don't make it to the end of October before putting it on, but will do this year! There are four of us in this house, and I am the worst for putting on the heating even though I'm layered up. I feel the cold more than the others.

But we're using 3000+ kwh a year without heating. I do cook and bake a lot, and my adult kids are guilty of putting the oven on to cook a pizza or reheat something. But I've cut back on oven use and still using more than most people.

Gas ovens don't use anywhere near as much as a boiler though. Just looked up the specs for my (average) gas cooker and the main oven burner appears to be rated at 2.5kw. A gas boiler is 10x that power rating. To use 3000kwh just on your oven it would need to be burning gas at full power for 3 hours a day. And they only burn at full power whilst heating up, so you'd have to leave it on gas mark 9 with the oven door open for 3 hrs a day to consume that much gas! Big burner on my job is 3kw, but again, I rarely use it on full power for more than a couple of minutes.

It's almost certainly your boiler that's burning through the majority of your gas usage, and unless people are taking really long showers while you're out, it's most likely down to central heating.

Depending on your household routines (who is at home, and when, throughout the day), you might find a smart thermostat useful. I've got Tado and it's geofencing is brilliant. It uses the GPS on your phones - so when I go out it automatically turns off/down my heating, and then turns it up again as I'm getting close to home. And the program on my thermostat is never higher than 17 degrees.

17 deg is chilly in my house! 19 is 'normal' with it being on 20 - 21 when it's really cold. We have a Nest thermostat - I will be really strict about it this winter. Hoping that I will see our 20,000 kwh come down from being less wasteful there.

We're at home all day - three of us WFH. Have turned hot water temp down again, so going to see if that makes a difference this week. Nobody's taking extra showers - maybe that happened a bit during the heatwave, but it's always four a day. I do nag about not using the hot tap to wash hands - pointless because the water takes so long to run hot and I imagine that adds up.

If your boiler has been serviced (properly not these half arsed services that some offer for circa £70), system flushed and radiators bled, it will be running as efficiently as it can. Unless you have done these things I wouldn't be replacing the boiler. You can also turn the flow temperature down if it is a condenser boiler which will mean it heats water more efficiently by using the heat from the steam it is creating as well as gas.

Gas is much cheaper than electricity, an electric shower won't save any money.

With regard to the boiler, it's highly unlikely likely that replacing it will achieve payback before it needs replacing again. My parents have a 40yo gas boiler that they're told every year should be replaced for something more efficient. I've had 3 boilers in that time. As with everything we buy these days they seem to have built in obsolescence. While it works, I'd keep it.

Yes, we've adjusted that - hopefully that will help too. I wouldn't want to replace it because we've had a boiler that was unreliable before, and this one has been really good.

Check you meter before and after showers - our shower uses about 1kwh of gas every 4 mins for the hot water. If 4 of you are having daily showers of 10-15 mins then that's going to add up. We've just got a 4 min timer to help reduce shower times.

We're averaging 250kwh a month with no heating on.

That does sound a bit off. We log less than that, and we’re in a drafty four-bedroom Georgian flat in Edinburgh with single-glazed windows!

Our showers are electric and so’s the oven and hob.

Is your hot water on-demand all the time, or do you have it come on for a couple of hours when you need it? I cut our usage a lot when I switched it from on-demand to twice daily.

I feel like replacing a boiler that’s working perfectly well is inefficient in the grander scheme of things. Plus what does a new boiler cost — two grand, two and a half? The new ones are good but they’re not magical and any cost saving would take many years to amortise, if it does at all.

But that usage does sound peculiar. Worth getting your boiler and heating system checked/serviced, to make sure there are no leaks or any other issues?

Combi boiler, so hot water on demand. We don't use the 'eco' setting - can't remember what it's called on ours, but it's something like instantwarm.

Have booked a service, but this isn't something new with the boiler which is why I'm wondering if there would be a saving replacing it. That said, I know newer models may use less energy, but I don't like the idea of replacing something that is working and reliable.

Not RTFT, but we have installed smart thermostats so we can control the temp of each room individually and schedule things, so we aren't heating a room no one is in or having a room heating to too warm while another isn't warm enough. Maybe worth a look if you don't have already?

I don't think that gas usage is bad at all though. We are 350 a month just for the hot water at the moment (I do like a deep bath though!) and that's a brand new Worcester Bosch.

My first post should have said 'smart thermostatic radiator valves'.

I've just checked our usage, it's 5743, how on earth is yours so high??

I have 2 teenagers, both like it warm, and take stupidly long showers

I believe the OFGEM typical usage is based on 12000kwh of gas, for 2.3 people in a 2 or 3 bed property. There are 4 of you, in a possibly slightly bigger house. So you can use that to help set your aim.

Before the boiler, look at the easy wins. What's the loft insulation like? Double glazing? Curtains? Does the seal round the front door need replacing? Do you/could you have cavity wall insulation

We're in a 4 bed detached in Scotland and gas usage is 13862kwh per year. We have gas boiler/hot water cylinder combo and gas hob. Thermostat set to 18/19⁰C when heating is on. Heating is on a timer (when it's on) for a few hours am and pm. Hot water only on for 1 hour per day.

Oven and shower is electric and appliances are cold fill. Our electricity usage is on the high side at 5845kwh per year.

@Cynderella we have similar living situation and use approx 4500kwh a year without heating which is more than yours.
I think therefore that your big spend/waste is going to be the heating.
I don’t think you would recoup much from a new boiler in energy savings compared with capital outlay.
I think the very biggest saving to be had in your home are changing how you heat your home.

Can you tell us how you would usually have your room thermostat schedule set with temps and times? Have you even got a room thermostat or is it all on the boiler?

@Cynderella

I don't think your shower usage is outrageous. 4 people 1 shower a day is 120 showers per month, so if you use 250 Kwh per month thats about 2 kwh per shower which is not unreasonable at all. If you use 20000 kwh a year total then you must be using 20000-(12*250)=17,000 kwh a year on heat. If your boiler is 25kw and you count winter as four months (120 days) then I guesstimate you have the heating on for the equivalent of about 5 1/2 hours per day. Which to me is a lot.

Boiler replacement is really hard to calculate, often older boilers ratings are compiled differently so it is really hard to compare. I'd guess with your consumption you might save as much as 4000 kwh a year or so with a new highly rated condensing boiler vs. a pre 2005 condensing one. But a 2008 model will almost certainly condensing and I would guess you would be lucky to save half of that if you swapped. IMO I don't think its ever worth swapping unless you are seeing significant repair costs every year due to age as well. You get a double whammy for something pre-2005, because not only do you get the extra efficiency, but also boilers that old tend to need more work.

We are 16,000 a year for a newbuild 4-bed detached, heating and hot water for baths and showers, so yours doesn't seem that bad for a an always-occupied Victorian property which won't be as efficient. You can probably shave some off by turning down thermostat a little and being more on the ball with turning on and off radiators when not being used.

5,000 gas is extremely and unusually low usage to that PP for heating a family home. It's way under the already conservative figures that make up the 'typical' household, so not really relevant.