Gas usage quadrupled?

WiserMiser

Presumably the boiler remains unaware that all the rooms are at or above the desired temperature, so it keeps burning merrily away until the return flow reaches the maximum permitted temperature.  It then cools down for a while only to fire up again a bit later on, despite no room requiring any heat.  Rinse and repeat until a room gets too chilly.

This continual short cycling is very inefficient, needlessly increasing your bills and won't do your boiler any good.  I hope there's a bypass, otherwise the pump will get hot and burn itself out because the water has nowhere to go when all the rooms are up to temperature.

Sea_Shell

But the system might not be the problem, if they are using it as they always have, and have noticed this spike in usage.

Has the OP done something different recently?

dharm999

Not done anything differently, everything is the same now as it was  a few weeks ago 

dharm999

Picture of the gas meter

dharm999

WiserMiser said:

Presumably the boiler remains unaware that all the rooms are at or above the desired temperature, so it keeps burning merrily away until the return flow reaches the maximum permitted temperature.  It then cools down for a while only to fire up again a bit later on, despite no room requiring any heat.  Rinse and repeat until a room gets too chilly.

This continual short cycling is very inefficient, needlessly increasing your bills and won't do your boiler any good.  I hope there's a bypass, otherwise the pump will get hot and burn itself out because the water has nowhere to go when all the rooms are up to temperature.

The boiler fires up regularly even when the heating and hot water aren’t on.  Our previous house had a Hive system, so installing something like that would then give me a thermostat which presumably would stop the short cycling?

FreeBear

dharm999 said:

WiserMiser said:

Presumably the boiler remains unaware that all the rooms are at or above the desired temperature, so it keeps burning merrily away until the return flow reaches the maximum permitted temperature.  It then cools down for a while only to fire up again a bit later on, despite no room requiring any heat.  Rinse and repeat until a room gets too chilly.

This continual short cycling is very inefficient, needlessly increasing your bills and won't do your boiler any good.  I hope there's a bypass, otherwise the pump will get hot and burn itself out because the water has nowhere to go when all the rooms are up to temperature.

The boiler fires up regularly even when the heating and hot water aren’t on.  Our previous house had a Hive system, so installing something like that would then give me a thermostat which presumably would stop the short cycling?

The Greenstar 40CDi Classic Regular has an output range of (nominally) 10kW to 42kW - Way too much for all but the largest of properties... Even with a half decent thermostat, unless you have a lot of radiators, the boiler will be short cycling quite a bit. Unfortunately, the 40CDi doesn't support a smart modulating thermostat (unless I missed it in the rather short manual). So you are limited to basic on/off control. Hive, Nest, Tado, etc will all work, but you won't be able to make use of some of the smart stuff that a modern thermostat can offer.

dharm999

The house is large, c350m2, and has 12 rooms plus 4 bathrooms, so needs a decent size boiler.  Have been wondering for a few months now whether it’s time to change it for something more modern and efficient that also offers more smart functions.  This might be what makes my decision to do it now before it gets cold and this becomes a far more disruptive problem 

FreeBear

dharm999 said:

The house is large, c350m2, and has 12 rooms plus 4 bathrooms, so needs a decent size boiler.  Have been wondering for a few months now whether it’s time to change it for something more modern and efficient that also offers more smart functions.  This might be what makes my decision to do it now before it gets cold and this becomes a far more disruptive problem 

OK. Fair enough. You probably have a 16-20kW heat demand, so even at a 10kW output, the boiler shouldn't short cycle. And with 4 bathrooms, I can understand why there would be a circulation pump for the DHW.

Your current boiler is only 10-12 years old, and has an efficiency of ~89.9% - A shiny new modulating boiler might get up to 94-95%, but you may well need to fit larger radiators in most of the rooms. Should you have micro-bore plumbing, you'll find that not all radiators can be increased.

Fitting a programmable thermostat that allows for different temperatures throughout the day/week could potentially save up to 15% on heating costs. In reality, more likely 5%, but that would still be a significant saving for you. A smarter control than can also turn the DHW circulation pump off at night (and during the daytime if the house is empty) will cut both gas an electricity consumption a bit more. That might push the savings up to 10% (or more in the summer months).

I used to have an old Baxi back boiler (only 13kW and ~70% efficient) that I fitted a smart(er) control system* to. Once the temperatures & schedule had been dialed in to my liking, I managed to cut gas consumption by 10-12%.

*) Home Assistant with a bunch of temperature sensors plus relays to switch boiler & circulation pump on/off. A steep learning curve, so not suited to everyone. Replaced the heating system a couple of years ago, but kept the H.A. system to control the boiler.

dharm999

Thanks.  House is modern, so no micro bore piping.  Was wondering if an air source heat pump might be a sensible option, as the house is well insulated, has UFH, and there’s a convenient space outside to put one.  That combined with smart controls could well sort things out for a good few years.  There’s also a plan for solar panels and batteries, and installing the ASHP may well accelerate that.

FreeBear

It would certainly be worth looking at an ASHP. But you may need a 3 phase supply and a big pump (maybe a 16kW unit). If you take your annual gas consumption and divide it by 2900, that will give you a rough idea of a HP rating. Although, with a pump circulating DHW, your gas usage is higher than it needs to be.

In the short term, fit a smarter thermostat, and get saving gas now.