The 2012/2013 graph shows the night outside minimum temperature in red and the daily amount of gas used in kWh in blue. The light red and light blue are for the 2011/2012 season. You can see how I've converted my meter readings to kWh here.
eTRV 'Sleep' button: Since February 2011, we have been using Chalmor eTRVs on all radiators. To make major savings in gas usage, we are putting many radiators to 'sleep' during the evening cycle (including bathroom, utility room, dining room etc. etc.) using the eTRV Sleep button while having them all on during the morning cycle.
This resulted in a 20% reduction in gas usage - a great result.
2013 Boiler Upgrade: In March 2013 I upgraded my old 25 year-old boiler and my gas consumption increased by 50% compared to previous years. Although, the boiler is much more efficient, several things conspired to create this result. You can see this quite clearly in the cumulative gas usage graph below. See below to find out why!
So now the crucial question to be answered is: "Does it use less gas?"
It has increased...
Reasons why gas consuption increased after the boiler upgrade: Up until the time of the upgrade in March 2013, I used eTRVs on EVERY radiator in the house including the hall. The hall is very large and is like two normal rooms in size really, so I used the eTRVs to turn heating in the hall off during the evening. This reduced gas consumption significantly but meant we had to rush from room to room as the hall was really cold!
The upstairs toilet did not have a TRV or etrv attached. The reason for this was so that flow was maintained through the boiler when all the eTRVed rooms were up to temperature. The downside of this was that the temperature of the water in the pipes was held high all the time that the boiler was switched on. The reason for this was that water temperature was controlled by the thermostat in the boiler. This is a very inefficient way of running things though this was perfectly normal back then.
A modern system MUST have a room (in my case the hall) with a wall thermostat that directly controls the boiler by switching it off when that room gets to temperature thus allowing the water in the pipe work to cool down. This also prevents the boiler 'hunting' (the boiler often turning on and off).
The direct consequence of this was that I HAD TO heat the hall, which is much more comfortable of course, but does significantly increase my gas consumption.
There is a way round this and this is by using a wireless thermostat system (such as the Honeywell Evohome system) that monitors each room individually and only when all rooms have reached their set temperatures does the boiler turn off. This means that I would be able to go back to how I had things before and have the hall at a lower temperature than other rooms downstairs.
I have now started experimenting with an Evohome system so I will let you all know how I get on with it!