Combi boiler costing more than previous system boiler.

flo22

annie42 said:

Thanks for all your replies. Will try and answer all questions. We now have an Ideal Vogue Max 32 which replaced an old system boiler with a Gledhill tank. The HE suggested a combi as there are just the two of and he said it would be cheaper. He gave us the option of a 32 or 40 but explained he’d need to uplift carpet to install new pipe work for the bigger boiler. He said the 32 would be ok so we went with that to avoid the inconvenience. There’s been no change to the plumbing. No new larger rads. The water temperature is 48degrees and the flow temperature to the rads is 60. We are in our seventies and not of the generation that has daily showers and baths. We have ten double rads and three single ones but seven are generally switched off partly because we have a large multi fuel stove in the kitchen the heat of which permeates other rooms. 

Feb -March 2023  Elec. 276.7kwh  Gas - 230 units.

Feb -March 2024 Elec 264.3. Gas 284 units. 

March -April 2023  Elec- 205kwh  Gas - 101units.

March - April 2024 Elec - 278kwh Gas. 166 units.

I have just checked all the rads and discovered my husband had turned on four of the ones normally off because of the continual damp weather which has cause a bit of mould around our draught sash windows. They were on but only so low I didn’t notice. So we’ve been heating ten instead of six. 🙈 Have I answered my own question? 

Have you checked what the units are?  when I had my boiler replaced I thought the new one was using a lot more but then I realised that the new units were in metric and the old were in imperial  - the bill had a formula for a correction value, I can't remember which way round it was but once I looked at an old an new bill side by side I could see it

ThisIsWeird

BarelySentientAI said:

Tall skinny stack vs short wide stack.  Same number of bricks.  The boiler only has to put in however much heat has come out of the radiator, so if both times the room is going from the same starting temp to the same finishing temp, the actual heat is the same.

Ignoring losses, which you probably can for this sort of rough analysis.

Thanks.

What I was pondering was if there was a situation where the boiler's output was just too low to get the rooms 'quickly' up to temp, so the boiler just ran and ran and ran; would this consume more gas overall? But I guess 'not', since it won't be producing as much output overall.

So, I can see no explanation for Annie's findings other than they are taking more energy from the new boiler, either because some rads have been left constantly on (albeit at a low setting), or they've started to enjoy deeper baths! Or, possibly, they have a new Prog Stat which has been set to given them a min overnight temp - say 15oC - whereas before they just turned the whole CH off?

Very unlikely the boiler itself is faulty or incorrectly set up in any way.

BarelySentientAI

annie42 said:

Feb -March 2023  Elec. 276.7kwh  Gas - 230 units.

Feb -March 2024 Elec 264.3. Gas 284 units. 

March -April 2023  Elec- 205kwh  Gas - 101units.

March - April 2024 Elec - 278kwh Gas. 166 units.

Not weather related as 2024 was warmer than 2023 in both February and March iirc

Albermarle

In January we swapped our system boiler for a combi having been advised it would save us money. Compared to the same months in 2023 we are using significantly more gas and electricity so much so Octopus is increasing our DD.

Amongst all the other sensible comments, I do not think that anybody has said that if the old boiler was pretty old ( > 20 years old) then a new condensing boiler should be more efficient and use less gas anyway, all other things being equal. Even if it was not that old a newer boiler should still be a bit more efficient.
Also I am not sure if it is significant that the OP will have changed from maybe a 15/18 Kw boiler to a 32KW boiler. This is perfectly normal when switching to a combi, but it does mean the boiler is more powerful than necessary for the central heating. I guess with all the modern controls it should not matter, but I do not know really.

annie42

Once again thanks for all your replies. I do appreciate everyone’s help. The heating is controlled by a smart Halo thermostat. It’s set for 7am - 10am then 4.30 - 10pm. It’s not on overnight at all. The CH seems to work as well as the old system did although I don’t know about the boiler run time during the timed hours. I will speak to the HE, explain the issue and amongst other things ask him if the CH output temperature could be too low. Re the readings I will check but a pretty sure the recorded units were and are in metric. 

ThisIsWeird

annie42 said:

Once again thanks for all your replies. I do appreciate everyone’s help. The heating is controlled by a smart Halo thermostat. It’s set for 7am - 10am then 4.30 - 10pm. It’s not on overnight at all. The CH seems to work as well as the old system did although I don’t know about the boiler run time during the timed hours. I will speak to the HE, explain the issue and amongst other things ask him if the CH output temperature could be too low. Re the readings I will check but a pretty sure the recorded units were and are in metric. 

If the CH system is performing effectively, heating up your house at a similar speed to the previous boiler, then there cannot be anything amiss that I can think of.
I'm not familiar with the Halo, but it might have 'optimum start' which automatically adjusts the start time so that you arrive at the temp you want at the time you desire. For instance, you have it 'set' for 7am, but it may come on well before this so it's 'at' the required temp by 7 am. So, if the flow temp is a bit low, the stat will have learned that it takes X hours to get to temp, so could actually be coming on well before 7am.
That's all guesswork, and tbh I can't see how this would use more gas anyway; it would be longer at lower output, rather than shorter at higher, so pretty much the same overall use. I think! And running cooler is more efficient.
I'm stumped. It's still more likely to be the extra rads that were on, coupled with deeper baths!
Please let us know what the HE says. 

FreeBear

annie42 said: The heating is controlled by a smart Halo thermostat. It’s set for 7am - 10am then 4.30 - 10pm. It’s not on overnight at all.

The Halo thermostat should support different temperatures throughout the day - It is worth setting (for example) 18°C in the morning, 19°C between 16:30 & 18:00, rising to 20°C until 22:00.

I have a baseline temperature of 16°C day & night with a morning temperature of 17.5°C, dropping back during the daytime, and kicking up to 19°C late in the evening. Before, I just had a fixed thermostat and a timer. Fitting the smart(er) thermostat, I got a ~10% saving on gas consumption. Had a new boiler fitted last year, and still use the same thermostat. If anything, gas consumption is up fractionally, but I've also increased the evening temperature.

I'd suggest reading the thermostat manual, and play with the settings to suit your lifestyle. A 60°C flow temperature should be pushing the boiler well in to condensing mode and get an efficiency of around 92%. Reducing the flow temperature isn't going to improve efficiency by much. Likewise, increasing the flow temperature by 5°C won't impact on efficiency (maybe drop to 90%), but will heat the house up fractionally quicker.

One (rather technical) question to ask your HE - Is weather compensation enabled, and what are the upper/lower bounds ?

On warmer days, having weather compensation enabled can lead to reduced gas consumption.

annie42

Many thanks for both replies. I will indeed ask the suggested questions also study the Halo instructions and let you know what the HE says.