gas usage trebled since installing Worcester 37CDi combi?

[dumbrill]

Its between -1 and -3 outside here at the moment, so I'm guessing its working pretty hard, but still, what I dont understand is how the old boiler can have been using so much less, I guess this must just be because it was a lot smaller and hence more closely matched to our current system.

What does everyone think about me turning the water stat down and only switching the water on when I need to use it? Not sure what setting to put the water on though as thought the "e" mode was meant to be the most efficient?

Are you really comparing apples with apples when you say it's gone from 6 to 14? Is it the same temp outside? Has the on time crept up, etc.

Look at the other way - if the 6 units per day is correct for the same conditions as we have now then you were only using 4.6kW to heat your house (aasuming the old boiler was 70% efficient). That doesn't sound credible.

If the hot water tank is insulated then the heat loss from it isn't a lot. There's little to be gained from restricting the 'on' time other than hassle.

 

[muggles]

Oh no, I wasn't expecting to be able to power both bathrooms at once, but there'll be more water based areas and i'd like to think it will be possible to use hot taps and have a shower at least and if the house is going to be 4 bed, then I don't want to be operating a boiler that's struggling.

So, I thought exactly what you were thinking about lowering the CH output on the thermostat, thats why I tried setting it to 3 but it wouldnt even reach room temp?? This is what is weird, how can this be a bigger boiler yet not even reach 20 degrees on setting 3? I now have it on 5 and its heating quickly yet not cycling so much Im not sure if this is good or bad

If it's a 4-bed do you not think that at some point both showers may be used at once? You'll probably get away with one shower and one hot tap running, one shower and two taps or two showers is going to seriously hit performance.

As for lowering the CH output, you misunderstand. I was not referring to reducing the temperature by lowering the stat setting, which won't really solve the problem, I was referring to going into the boiler's settings and reducing the power of the boiler. It's currently 37kw(ish) but, if the feature is available, could be lowered to say 20kw on the CH side if this is more appropriate. This can then be raised up again when your extension is built.

 

[pooch251081]

Does 6 cubic meters equate to 4.6kW? Not sure how thats possible, if my ravenheat had an output minimum of 7-8kW and max 24kW and I had it set to around two thirds of full? Sorry, maybe I'm getting something mixed up here? I know that the 6 cubic meters is around 66kWh but this is a different unit, no?

 

[pooch251081]

muggles, thanks for that, it sounds a great plan but I didnt know that was an option, any idea how thats done at all as I would have no idea? Not related to the pump speed is it??

 

[pooch251081]

Should probably mention something the installer also mentioned, that our boiler is housed in an outbuilding that is really cold and the indoor pipes are not lagged. Should i be concerned that the water in the pipes is so cold this is taking longer to heat or even that when i turn the boiler off it may be needing to fire to protect itself from the cold?

 

[muggles]

You'd need to go into the settings program, it'll be in the instructions somewhere (if this is a feature, not overly familiar with WB boilers, it may not be possible)

Lagging the pipework will help if the boiler's in an outbuilding, and the boiler does have auto frost protection so it'll fire to keep warm. If there's pipework runs out there it should also have a frost stat connected to a pipe stat to fire the boiler if the pipework temperature drops too low.

 

[eddiespaghetti]

If its cycling, there's a good chance you're ****ing a load of unburnt gas out into the air each time the regulating valve opens and closes, this might account for some of your missing gas!

It's a case of matching the incoming gas pressure to the load, on my ancient Baxi there's a screw which dials down the incoming gas pressure (and hence flow) into the burner. It's a non-modulating boiler which gives me about 2kW leeway, which came in handy when I had some rads off for decorating.

It's worth downloading the installation manual from their website, it'll be fairly obviously given as a table of pressures versus outputs.

You also say the system is balanced, but its worth checking the manual again to check the recommended deltaT across the boiler and rads. What type of thermometer was the plumber using to measure the deltaTs on the rads? Looking at the manual, that boiler's designed for a 20degC deltaT. Have a quick read through the troubleshooting, section, if your return temp is too hot, your boiler'll shut down before your rads are anywhere near rated output and you'll not get any condensing.

 

[dumbrill]

Does 6 cubic meters equate to 4.6kW? Not sure how thats possible, if my ravenheat had an output minimum of 7-8kW and max 24kW and I had it set to around two thirds of full? Sorry, maybe I'm getting something mixed up here? I know that the 6 cubic meters is around 66kWh but this is a different unit, no?

6m3 equates to 66kW/hrs and you have the heating on for 10 hours. Assuming an old boiler at 70% efficiency then that's 4.6kW actually converted to heat the radiators.

 

[pooch251081]

I will check the manual, if I cant find it, should I call Worcester and ask if this is an option? I've got a feeling it might not be an option as I've gone through that manual with a toothcomb but will definitely look. Again, does this have anything to do with pump speed at all?

 

[pooch251081]

Ah ok, so yes thats probably about half the output that could possibly be fed into the rads then as i worked out they can take 8kW, I'm pretty sure they definitely werent at full heat as they werent scolding hot so is this not feasible then?

 

[dumbrill]

I will check the manual, if I cant find it, should I call Worcester and ask if this is an option? I've got a feeling it might not be an option as I've gone through that manual with a toothcomb but will definitely look. Again, does this have anything to do with pump speed at all?

To be honest I don't think your comparing like with like. I can't see how you could heat what you have described as a not particularly efficient house in conditions like we have now with only 4.6kW. And that figure doesn't account for other usage such as water, etc. The 6 units/day can't be correct for current conditions. I think simond got it right in the third post.

 

[ianniann]

The manual you most likely have will not tell you how to adjust the pump speed, or how to range rate your boiler, but it can do both of these things. You need to go into the tools menu (hold down the spanner button), but you also need to know the codes for the settings you want to change and I don't have these to hand. The default pump setting is a proportional one which is suitable for most situations with TRVs fitted. You can turn it down to a lower proportional setting but it doesn't make a massive difference.

The "e" setting on your hot water is relatively meaningless. Off the top of my head it corresponds to heating the water to about 50C which allows the boiler to condense well but still produce a good water temperature for a shower. There is relatively little to be gained or lost from changing this. Set it so that your hot water is hot enough for what you need.

With solid walls, no way that 6 units a day would heat your house. I think the 15 (nearer to 20?) is about right for the conditions. Compare your usage to the cold snap last January and see what your usage was then. The rate your rooms heat up is almost entirely controlled by the temperature of the radiators which has very little to do with the power of the boiler. Every combi boiler is far more powerful than necessary to keep your radiators at 60C or even 70C. If they don't work so well, or the boiler is constantly cycling, at 60C then turn it to 70C. The boiler control is relatively insensitive, with 4 being 60C and 5 being 70C with nothing in between.

 

[pooch251081]

Ok well I just checked online and I just got my gas bill from the last month (details shown below) which to be fair has been pretty darn cold. This was from the old boiler, and you can see I used 5 units a day according to this, on average? And i've had it at 20 degrees every evening so this must be enough to heat the house! Hence, I cant understand why now this has trebled!

27 Oct 2010 - actual 1320 You gave us your meter reading
25 Nov 2010 - actual 1469 You gave us your meter reading = 149 metric units over 30 days (actual) Gas units converted = 1666.22 kWh used over 30 days Usage charge First 220.00 kWh x 6.354 p = £13.98
Next 1446.22 kWh x 2.926 p = £42.32
Total cost of gas used £56.30

 

[ianniann]

Here you go. Tools menu item 1.A is for range rating the heating output. The default (full output) is 83, meaning 83% because the 37kW CDi maxes out at about 30kW for heating and 37kW for hot water. You can drop it as low as 32% I think, which means your radiators will take longer to reach operating temperature but the boiler will run for longer and cycle less. You change the value with the two lower buttons on the left hand side, and then save the setting by holding down the funny ladder button for a couple of seconds until the display flashes. Maybe turn it down to 50% to start out with and see how you like it.

The pump setting is 1.C. The default 04 is proportional pressure, high setting, useful for larger houses with TRVs. 05 is proportional pressure, low setting, better for smaller houses with TRVs. 01 is constant high pressure, 02 medium, and 03 low. There is not an enormous difference between them all but 05 might be better for you. 00 is a constant power setting which you can use to have a huge difference but I suggest you don't get there with a ventional radiator heating system.

Really your installer should have adjusted these things to match your installation. I'd suggest just putting the heating on setting 5 and seeing how that goes befire you mess with the tools menu.

The human mind is a wonderful thing and quickly forgets that the second half of October and the start of November was abnormally warm. I used a lot less than 5 units a day back then and now I'm using about 10, so I see nothing wrong with your gas usage. Still, try to get your heating working well and maybe you can get it slightly lower.

 

[ianniann]

Another thing to be aware of with this boiler. By default, the hot water internal to the boiler is maintained hot (most combi boilers do it). This requires the boiler to fire possibly every 20 minutes or so although it often won't fire every time if the water is still fairly warm. This uses approximately half a unit of gas per day (possibly more if your boiler is in a very cold location), but it gives you hot water more quickly and you waste less cold water while waiting for it to go hot. The 37CDi is so powerful that you may find it works just fine with this feature turned off. Press the ECO button until it lights up. I know! Shine a light 24/7 to tell me I'm saving energy, duhh!! If you frequently use small amounts of hot water then you may want to let it stay hot.