Gas Consumption - Vaillant ecotec combi boiler 831

[Harry Potter]

I do believe my combi boiler is economical but I am curious as to how much gas it consumes and the best way to use the boiler.

What I am after finding out is - how much gas does the boiler initially use when I switch the heating on when it has to heat up the water in the expansion tank (correct me if I am wrong). At that start point, does the boiler use a lot of gas to hot the water up that runs through the radiators and after that, almost no gas? Or is it a steady amount of gas at all times when the boiler is on?

Earlier I had the heating on for maybe 10 minutes until my radiators got hot then I switched it off. In that time I had used a ninth of 100th of 1 unit of gas. (I have 11 radiators but only 4 on).

Any help would be much appreciated and thanks in advance.

[big-all]

its simple enough really you have to heat the mass off the water up in the radiator and pipes then the heat gets transfered to the room
all actions off the boiler cost money whilst its giving heat

[Someone-Else]

Why can't you do as it appears you have been doing, watch the gas meter.
To check how much something uses you need to meter it, since its gas you are interested in, your house may have more or less insulation than mine (For example) so the best way to see how much YOU use is to watch your gas meter. (Not exciting I know)

[Harry Potter]

Thank you very much for your replies and I will keep watching my gas meter.

[Harry Potter]

Me again, I do have good loft insulation and wall insulation but dont think the wall insulation made a lot of difference. My living room, 15' x 12' has wooden floor boards but a good underlay and axminster carpet.

Windows and doors were replaced in 1993 so I dont think they are as effective as they once were but it would cost a lot of money to replace them, even though the specification will be much better 24 years later.

[ericmark]

It has been talked about a lot, with a condensing boiler the flame height can be adjusted, there are two basic methods, one is to use the return water temperature, as the return water temperature increases so the flame height reduces, however there are flaws in this method.
1) Once it hits minimum output the boiler starts to cycle, however on switch on instead of a low flame height, most start again with high flame height so all pipes are also heated to a high temperature and so more energy is used than required in many, no all cases, and energy is lost also through the flue.
2) There is nothing to tell the boiler switch on now you are required, the only way boiler knows if required is to switch on anyway so again energy wasted.

Fitting a thermostat can shut down and start up boiler, however a single thermostat in the main can't monitor multi-rooms and it can cause the TRV to open too wide so on turn on the radiator gets too hot, there are some thermostats which use the temperature recorded by the eTRV head EvoHome is an example, however it is still trying to mix the analogue control of the boiler and TRV with a digital control, not ideal.

So we have method two, this is where the boiler eBUS is connected to a controller so the boiler only fires up when really required and in cold weather the water returned is hot and in hotter weather the return water is cooler this is the right way around as when it does turn off the boiler is cool so less heat is lost, again EvoHome also has the option to connect to eBUS of boilers using the OPenTherm protocol.

However not all boilers use OpenTherm protocol either not having a connection to the eBUS or only being able to use their own products, now we come to second problem, the whole idea is each room is independent, using something like EvoHome we can do that, but with some systems you only have one modulating thermostat, great with open plan home, but fit doors, and it simply does not wotk.

The problem is living in the house we can adjust lock shield valves, and slowly tweak TRV so they match any wall thermostats, however the installer does not live in the house, he can roughly set the lock shield and roughly set TRV's but he simply can't spend the time required to tweak the system, his only option is again something like EvoHome which does it automatic, using cheaper options is not going to be some thing he can set up, it is down to the user.

Now I know with a Non OpenTherm boiler by having a thermostat and TRV in the hall I have been able to set heating to work reasonably well, but also having a TRV and wall thermostat in the same room can be a complete failure, it needs setting up so carefully, it also means any idea of altering temperature through the day is out, all you can do is on/off, well OK can have a anti-frost setting but since thermostat on the wall needs to match that on radiator and the latter only has numbers once set you just leave it alone.

There is another problem with on/off wall thermostats, if it is used with an old pre-condensing boiler we wanted it as it reached the target temperature to start cycling so it would not over shoot, but working with a TRV we don't want this feature, OK with hard wired thermostats just buy a cheap on. However cheap wireless do not have auto shut down should batteries go flat, so buying one with the auto shut down means it also have anti hysteresis software built in.

I would like this year to do a further test, at the moment the TRV in the hall is a low quality one which has been set to match the wall thermostat using the pins in wall thermostat so when turned down it can be returned to exactly the same temperature. It works, however at night heating is turned off, with a second thermostat in kitchen over riding the programmer if the night is very cold.

I would like to try a programmable thermostat and a programmable TRV together to see if the temperature can be dropped over night rather than just switched off.

[dewaltdisney]

It all depends on how hard the boiler has to work. A well insulated house is like a strorage heater in that the walls warm up retaining a degree of warmth that keeps the room temperature warm so the boiler has low burn cycles to maintain the set level of temperature in the room. This is if the heating is on 24/7. I have been using this method for a decade now and we heat all rooms leaving it running on a thermostat. Warming up a house from cold requires a lot of heat but maintaining a level of heat seems to be far less use of the boiler. So I think perceived thrifty use does in fact cost more in the long run.

My gas bills have been fairly consistent at around £60 a month for a four bed detached house. Of course being retired we spend more time at home so this might not work for you but a version of this method with careful us of a thermostat might well work.

DWD