getting the best from a combi

27 Sep 2011
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United Kingdom
After having a WB 30cdi combi installed in October 2011, my recent gas statement would suggest that it's using more gas than the old back boiler by around 10%.

I've read through this forum which has just confused me even more, with conflicting advice being given to people also seeing a rise in useage since having a combi fitted.

As understand it, it's best to have the TRVS open to stop the boiler cycling, which they already are.

The key point seems to be the temperature of the returning water to the boiler. It's a condensing type boiler, very efficient I was told, but I'm still confused what the returning water temperature should be to get the best from the boiler.

As the boiler is in an outhouse, I've recently lagged the pipes with that silver bubble wrap, but checking the meter is suggesting that I'm using even more gas now, 8.42 units per day over the last 19 days compared to
5.48 per day in the preceeding 114 days.

Has lagging the pipes simply meant that I'm now returning hotter water to the boiler than I was before, which I thought was a good thing, but clearly isn't.
Does this affect the condensing function, which I thought reused the hot fumes that would usually be vented to air.
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If you are using more gas it means you are supplying more heat to the house.

However having said that the condensing boiler should be more frugal with
the gas for central heating.

Do you have a wall thermostat in the house to switch the boiler off once the house has got to temperature?

Personnally unless there was a reason to change you were better off with the back boiler for reliability.
Many reasons to take the back boiler out, but anyway it ain't going back in.

When the boiler was installed, a room stat was not considered as essential, however it would appear that it is.

The last statement, winter, showed a credit of £35. Great, I'm saving money already with this new combi.

The recent statement, Jan-May, is now £28 in debit. The only change has been warmer weather, figure that one out, and me lagging the pipes to and from the boiler.
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A Room Thermostat has been a LEGAL requirement of Part L1 of the Building Regulations for MANY YEARS NOW!! there should be no TRV on the Radiator in the room containing the Room Stat the room stat will shut down the boiler once the house is sufficiently warm therefore saving cash, the boiler will fire when the temperature falls and will fire from cold aiding condensing operation ;)
I suggest fitting a combisave [/url] These devices reduce the flow r...180 fitted. The actual valve costs about £80
As understand it, it's best to have the TRVS open to stop the boiler cycling, which they already are.
Leaving them open means you might as well not have them at all. The whole point is that they will close when the room temperature reaches the desired level.

That and no room thermostat will just result in the boiler running all the time, and therefore using far more gas than necessary.

The temperature of the water returning to the boiler is determined by several factors, such as the boiler being correctly sized for the heat output required, and having radiators of a suitable size for each room.
As the installer neglected to install the essential room thermostat, who knows what else wasn't done properly.
I always have the TRVs set to whatever temperature i wanted in each room, but reading too many forums seemed to suggest that having the TRV left open was the way to go. Not having a room stat would make this a daft solution, I see that now, so won't be taking that advice.

I used to have a room stat when I had a back boiler, so did wonder why I shouldn't have one now.

Needless to say, I'll be getting one installed. Wireless ones seem popular.

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