Pilot light and general gas consumption

[giw12]

Morning All

I've been on a mission to prove to myself how inefficient my 43kw Potterton Osprey boiler is (I've posted on it recently) and I'd appreciate thoughts on my latest detective work.

Over a 12 hour period of no boiler activity, the pilot light notched up 0.4 units on my imperial meter. This scales up to an impressive(!) 146 units pa or just under 4600kWh (this is about 300kWh more than my entire year's higher rate amount and would equate to £160 p.a. at the winter month's rate).

I'm staggered to be honest!

This all contributes to my annual usage of 37,500kWh - a 4 bed house (15 rads) that's kept at 19 degrees from 07:30 to 20:30, with a fairly average size hot water cylinder that's heated to 55 degs three times a day for 30 mins each time.

I think there's something fundamentally wrong here and I'd appreciate you thoughts/views/sympathy!

Thanks

Gary

 

[D_Hailsham]

Over a 12 hour period of no boiler activity, the pilot light notched up 0.4 units on my imperial meter.

Are you sure you have measured it correctly? When you say that 0.4 units were used over 12 hours,which numbers were you reading?

Imperial meters measure in cubic ft. There are usually four black numbers, two red and a dial. The right hand black number goes up in units of 100ft³ and the right hand red number moves in units of 1ft and the dial rotates once for each ft³. So if it reads 123456 it means 123,456 cubic ft. When meters are read only the black figures are recorded, so a reading of 1234 means 1234 hundred cubic feet.

 

[giw12]

It's a cubic feet meter and has 4 black digits and 2 red (though the second red one is '0' all the time i.e. it doesn't move).

The reading at 8pm last night was 9830.80.
The reading at 8am this morning was 9831.00.

In a 12 hour period then I reckoned this is a usage of 0.20 units.

Have I read it correctly?

 

[Agile]

A pilot light uses about £30-£40 of gas per annum.

However, for much of the year this contributes to heating so is not all lost. However, newer boilers dont have pilot lights to make them more efficient.

There also seems something wrong with your house if you have a 43 kW boiler!

Most four bed detached homes need about 12-18 kW for heating plus an additional 2 kW for water heating so a 24 kW boiler is more than adequate!

Seriously oversizing the boiler will greatly increase the gas consumption!

A typical gas bill for a four bed detached house would be £1000-£2000 pa.

Tony

 

[D_Hailsham]

It's a cubic feet meter and has 4 black digits and 2 red (though the second red one is '0' all the time i.e. it doesn't move).

The reading at 8pm last night was 9830.80.
The reading at 8am this morning was 9831.00.

In a 12 hour period then I reckoned this is a usage of 0.20 units.

You seem to be reading it correctly, but it is strange that in your first post you said it used 0.4 units in 12 hours and now you say it used 0.2 units. Do you have a gas hob or gas oven? Strange that the second red dial never moves - have you watched it to make sure it never moves?

According to the formula used to calculate the seasonal efficiency of a boiler (SEDBUK rating), a permanent pilot light reduced the efficiency by 4%.

 

[D_Hailsham]

There also seems something wrong with your house if you have a 43 kW boiler!

This is really a continuation of the conversation the OP started under the title Boiler Efficiency (or not!). We have already ascertained that he only needs a 25kW boiler and even smaller if he insulated the house.

 

[Agile]

So it is! Some things never change!

He may have miscalculated the cost of the gas because the Imperial "Unit" of 100 ft³ is converted into kWH for charging purposes. The sooner people stop talking about these "Units" the better!

Tony

 

[giw12]

It's a cubic feet meter and has 4 black digits and 2 red (though the second red one is '0' all the time i.e. it doesn't move).

The reading at 8pm last night was 9830.80.
The reading at 8am this morning was 9831.00.

In a 12 hour period then I reckoned this is a usage of 0.20 units.

You seem to be reading it correctly, but it is strange that in your first post you said it used 0.4 units in 12 hours and now you say it used 0.2 units. Do you have a gas hob or gas oven? Strange that the second red dial never moves - have you watched it to make sure it never moves?

According to the formula used to calculate the seasonal efficiency of a boiler (SEDBUK rating), a permanent pilot light reduced the efficiency by 4%.

Apologies...the actual reading was 0.2 over 12 hours and extrapolated to 0.4 over 24 hours. My calculations though were based on the correct readings so the £s are all still correct.

The second red dial isn't even a dial..it's a graphic .I've taken a piccy:

Meter

• giw12
• 1 Apr 2009
• 1

I don't have any other gas appliances in the house.

 

[giw12]

I've not been hiding the fact I've posted on my boiler earlier.

What I'm trying to establish with this post is whether or not there's a fault somewhere given the amount of gas my pilot light seems to be using.

On the subject of the boiler itself (installed by the previous owner), I don't think there was ever any conclusion on whether it's worth getting rid of the Osprey right now or waiting until it requires an expensive repair.

Hopefully I'm reading my meter incorrectly but I don't think I am.
My annual calculations for the pilot light are:

0.4 * 365 (days)
= 146 (units p.a.)
*2.83 (cubic meters)
=413.2
* 1.02264 (conversion factor)
=422.5
* 39.1 (calorific value)
=16521.1
/ 3.6 (convert to kWh)
= 4589.2 kWh.

Is this correct?

And, assuming there are no leaks, is my boiler using such an obscene amount of gas that I should replace it straight away?

Many thanks

 

[D_Hailsham]

Hopefully I'm reading my meter incorrectly but I don't think I am.
My annual calculations for the pilot light are:

0.4 * 365 (days)
= 146 (units p.a.)
*2.83 (cubic meters)
=413.2
* 1.02264 (conversion factor)
=422.5
* 39.1 (calorific value)
=16521.1
/ 3.6 (convert to kWh)
= 4589.2 kWh.

Is this correct?

Your calculations are correct and you are reading the meter correctly. So the question now is why so much gas? Are you sure the boiler never lit over the 12 hours?

Turn the boiler right off, including the pilot light and watch the dial on the right to see if it moves at all - you may have to leave it for an hour or so. If there is any movement, there is a gas leak somewhere - time for Transco.

If no gas leak, relight the boiler but leave the HW and CH off at the timer. Then check the pilot consumption again.

 

[giw12]

OK, as of 12:30 a everything (including pilot) is off.

Meter shows:

Untitled

• giw12
• 1 Apr 2009
• 1

The red dial is at '9'

See you at 13:30!

Thanks

 

[Agile]

How "big" does the pilot light look? A domestic boiler usually has one about 25-30 mm long. Many commercial boilers had much bigger and floppy looking pilots and 50-60mm was not uncommon!

Has the boiler been serviced by anyone who really understands boilers? Its quite possible yours is set too high!

This is a commercial boiler in terms of its usual useage. Some of them did have very large pilot lights and that was not very important when gas was cheap and in a normal usage the gas consumption would be £3000-£5000 p.a. so £275 is not such a large amount.

Unfortunately data on pilot light consumption is just not available. Perhaps someone reading this with an old boiler can measure their consumption and see how it compares with yours.

I have forgotten what your annual consumption/cost was so the saving of a modern boiler correctly sized could be considerable.

Tony

 

[giw12]

One hour in and no movement in the meter:

Untitled

• giw12
• 1 Apr 2009
• 1

Pilot light now lit and CH/HW both off!

 

[giw12]

How "big" does the pilot light look? A domestic boiler usually has one about 25-30 mm long. Many commercial boilers had much bigger and floppy looking pilots and 50-60mm was not uncommon!

Has the boiler been serviced by anyone who really understands boilers? Its quite possible yours is set too high!

This is a commercial boiler in terms of its usual useage. Some of them did have very large pilot lights and that was not very important when gas was cheap and in a normal usage the gas consumption would be £3000-£5000 p.a. so £275 is not such a large amount.

Unfortunately data on pilot light consumption is just not available. Perhaps someone reading this with an old boiler can measure their consumption and see how it compares with yours.

I have forgotten what your annual consumption/cost was so the saving of a modern boiler correctly sized could be considerable.

Tony

Hi Tony

I've just relit the pilot and tried to have a look of it but it's very hard to see (it looks like there may be more than one?)

The boiler was recently serviced by a CORGI guy who came highly recommended and has been around for a long time. He commented that he's been fitting boilers in this area and even though there are some seriously big houses round here he has never fitted anything larger than 100,000 BTUs. Mine is rated at 150,000.

From 18/1/8 to 18/1/9 I used 1192 units (37,500 kWh) which is way beyond all the guide figures I've seen for 4 bed houses (usually 20-25k).

Do you think there is a compelling argument to change my boiler straight away?

Thanks

 

[giw12]

One hour in and no movement in the meter:

Untitled

• giw12
• 1 Apr 2009
• 1

Pilot light now lit and CH/HW both off!

OK...half an hour in and the clock face-type dial (on the right) has now rotated 180 degs and is pointing at the '.1' position (i.e. the first mark after the 12 o'clock position).

Pic added for completeness:

Untitled

• giw12
• 1 Apr 2009
• 1

Can anyone tell me how the clock face dial relates to the numbered dials?