Cause of sudden gas usage increase

Hi there

I recently noticed a tripling in average daily gas usage and am trying to tie down the cause. I have gas ducted heating underfloor, a gas hot water system and gas hob. With all those not operating, the gas meter reading was not moving. No smell of gas outside. The heating has not been used any more in the last few weeks compared to previous months. The only thing I can think of is that something could have changed when the ducts were cleaned a few weeks ago. Perhaps something was knocked. Anything else I should check? Thanks forxany suggestions.



Check your bill to see if it was an actual reading taken of the usage…or an estimated usage for the bill. If estimated, they may have overestimated it and one can usually call them with a meter reading to rectify.


The usage is based on my self readings and dynamically updates the daily usage on the app.


A good place to start. There is a possibility as you suggest the usage is due to something arising from the cleaning work. Was the heating working poorly prior to cleaning reducing airflow and thus gas usage, or has the contract left something venting and loosing heat from the system? The gas heating will as you probably know from your daily reports be the main user of your gas supply.

One option of you know the install well is to thoroughly inspect all of it, or have a professional inspect the system operation.

A simpler starting point could be to make do without the heating for a 24 hour period to confirm that usage for the hob and HWS is as per normal. This will demonstrate or narrow the likely cause down to the ducted heating, if you can produce the daily numbers. Calling the cleaning contractor to come back and check for any error is also an option. Some businesses are reliable and will oblige for free. Those that will not make their own future. IMHO.

As @phb suggested, being confident of the meter readings is also important. Assume you can read these manually from the meter face to do your checks, just to be doubly sure.


It is best to turn off everything, take a meter reading…wait as long as you can (hours or overnight) and then take another reading before switching anything back on. This will give an indication of any losses due to leaks.

Also, in cooler periods, consumption will increase as more heating is required. Comparing say autumn to winter months may also give a false impression of losses/additional use, as one would expect a higher use.

The recent maintenance may have also cleared any blockages making the heating run better…this could also mean higher use. Have you noticed your heating performing better…say hotter or quicker to heat.

Also check that by accident the direction of flow was not changed…such that some heated air now vents externally. This can be checked by turning the heater on full and seeing if warm air is venting externally through and fresh air intakes. If this is happening, the heater will be overworking and using more gas.

Has the app recently been updated with a new version?

Have you manually read the meter and compared it with the app/bills?

Does the app have a pressure correction?


An obvious thing to check is whether one of the ducts got knocked off and is heating your underhouse. Easy to check that all the ducts are properly connected to their outlet vents…


This would be my first thing to check. Examine all the ducts and joins while the system is running.


It’s a really tight crawlspace under the house. Would need a boilersuit and equipment to look myself.

I checked all the external vents and nothing blowing out. The external heater itself though is blowing out a lot of hot air.


This doesn’t sound right…assuming you mean releasing to the atmosphere.

Maybe call the company that did the maintenance as it could be that they accidentally changed something while doing the work. It may be a dudt shut off causing a back flow out at the heater end.


You do not need to crawl anywhere. Just turn it on and go to each vent to confirm it is blowing an expected amount of air. In some vents you can actually see the ducting where it attaches.

That will catch major fails but not necessarily tears that might have happened.

As @phb noted that doesn’t seem right, but it is not clear if you mean blowing air into the ducting or into the open air. Heaters should not be blowing into the open air, just venting heat and fumes from the burner.


Yeah, the heat is coming out of the vent on the front of the heating system and putting about as much heat into the air as into a room.

I checked inside all the internal vents and they seem ok and the ducts are attached.

I will call the cleaning company.


This is where the additional gas consumption is going.

If they caused the problem, it is their responsibility to rectify (at their expense).


That may or may not be the problem. I assume that the gas burner has its own external exhaust flue, ie it doesn’t send the burnt gas into the house. Can you determine if there is a separate vent elsewhere for that purpose? If not the hot air vent you are observing may be the normal flue and not leaking circulated hot air.


Assume you have a user manual and product brochure for the system. It should include some guidance on the capacity of your unit and gas consumption to expect. The units vent externally. For the same reasons gas HW heaters need to be installed externally. (At least where I live.)

It’s worth considering the system has two air piping connections to the house. One to deliver hot air and another that draws air from the house into the heater. There could alternately be an issue with the air return connection to the outdoor unit. This could cause it to be drawing in fresh cold air to heat rather than the warm air from the house, to reheat. More efficient, less gas to reheat. Is there a fresh air change over for the system that may have been left open? Or simply a damaged connection on the suction/intake side.

As much as we sometimes like to fix things ourselves, it’s not always within our individual experiences to do so. If nothing obvious can be found, going back to those who did the cleaning (and should be qualified with gas heating systems) is a common thought here.

For general interest one brand’s product brochure for those not familiar with the heater or general design.




I am not sure what this graph means. The bars are remarkably uniform, the usage is the same for weeks on end. Then it say “Values are estimated averages”. Why are they estimates and how are these derived? Why averages, averages over what period? It looks to me that this is not actual usage at all but a projection. I wouldn’t get too excited until you find out what your actual usage is.


The graph adjusts every time you do a reading. So it just averages the days between each reading and they end up the same figure, unless you take a reading every day. So it can change a little bit as your usage increases or decreases but never with such a sudden jump. So it’s pretty much been consistently in the range 250-350 since April when I first switched the central heating on.


What date was the service done?


Afternoon Thu 9 July.

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The screen shot has disappeared…how does this compare to when consumption jump up on the graph?