Low Gas Pressure

[Private Enquirer]

I was a little concerned about the gas pressure at my cooker hob so decided to test exactly what was happening before deciding whether to call a CORGI engineer or Transco/British Gas as I do not want to get fobbed off by either as I like to understand what is happening first.

We had a new condensing boiler fitted about 4 years ago by British Gas - a large one badged by BG but probably a Worcester Bosch 40 HE Plus with a slightly higher heat output spec. They upgraded the gas supply pipes to 28mm from the meter to allow for pressure drops while running. Our gas cooker T's off this somewhere in 15mm I believe. All working fine!

Two years ago we had a new gas meter and regulator/governor fitted as part of the gas mains upgrade in our road in plastic.

Last week during very cold weather I measured 22mBar static pressure using a conventional water gauge at the gas meter test point. When the boiler fires up the working pressure drops to anything between 16mBar and 18mBar still at the gas meter depending on how large a flame is being demanded by the central heating system. I therefore detect about 5mb drop just at the meter.

I called British gas this week when the temperature was very much warmer and they came within the hour. He showed me his water gauge readings (all at the gas meter as before) and they were totally different from mine last week. The static pressure was 24mb and the working pressure was 19mb when the boiler was running full. He got the same sought of drop in pressure I had found (i.e about 5mb drop) but from a much higher static pressure.

He seemed a bit officious and said mine was his third similar visit that day and he blamed CORGI engineers for taking wrong readings. He thought my governor was the best brand new type available and should be correct. He said if the working pressure was below 19mb he could adjust the governor (I thought they were not supposed to do that).

After he had gone I re-tested it myself and got very similar readings. I found the static pressure was even up to 25mb today and I confirmed his

19mb working pressure.

I think we were both right on the different days as I had measured it low last week when the only thing that had changed was the ambient temperature which was much colder then. Does the gas pressure change much with weather temperature and overall demand in the street?

I cannot get them to do anything today so am stuck with what I have got for the time being. Everything seems to be working OK.

What do others think.

[Andrew Mawson]

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I had a similar problem just before Christmas two years ago. Pavement works dragged out my steel gas main. Transco insisted on pulling a plastic pipe up the old one then wouldn't reconnect my appliances as the pressure drop was too high. They went through three cycles of pulling a bigger plastic pipe though before concluding I needed a bigger meter (BGas had checked the boiler every year for ten years with no issues!!) Wanted me to pay for a bigger meter. Eventually resolved when I dragged the Transco big cheese out of a meeting in Paris to give him a bollocking (hehe). However I'm personally convinced that the problem was relatively low pressure in the street main due to high demand and there was no problem with either the pipe of meter.

AWEM

[cynic]

Ye canna change the laws of physics captain

Under exceptionally heavy loads such as everyone running boilers simulataneously the dynamic pressure in the gas mains will reduce due to pipe friction losses. This is not helped at all by multiple large instantaneous demands from high flow rate combis when hot water is called for (hot water storage systems are much more forgiving) It comes down to the gas distribution infrastructure. If this is a regular thing then there is an argument for Transco to rip up the roads, replace the pipes with larger etc etc. Of course Vladimir Putin may also come into the equation!

[Private Enquirer]

That (and the other poster) is the best answer I have had so far. BG may have official published specs agreed with CORGI but it is clear that I am seeing problems with their distribution. On the cold day with big demand my governor had not actually cut in to do its job and all I was seeing was direct pressure fluctuations in my newly plastic lined old iron pipe. They re-laid the gas big street main using a push in plastic liner which is obviously smaller than the original iron pipe. I should have called BG out on a cold day to get a more realistic reading. The evidence was lost on a warm day and everything appeared to me normal, although I suspect I should not see a 5mb drop at the meter if the actual street supply is up to spec.

Thanks for that explanation

[RW]

If it ain't broke why try to fix it?

Does everything work as normal ? if so why worry .

[Ed Sirett]

No. You need to see the difference between the running pressure when the smallest hob ring is on it's lowest setting. The standing pressure (24mb) just tells you that there is at least 24mb in the service main.

No. You and I are not supposed to tamper with that but he may.

Quite probably, not all areas, not even most will have a problem. It's far worse in Bulgaria ;-)

What's happening at the hob. Can you see the flames alter? Do any of the rings go out when on minimum?

[Andrew Gabriel]

I bet they don't bother to purge the the whole network and everyone's home pipework before allowing it back on;-)

[Ed Sirett]

Never having being to Bulgaria I don't know what type of equipment is commonly used. It might well be industrial type kit and communal heating.

[ARWadsworth]

Sorry for the late question, I have been away for a few days, but what would happen in this country if a sizeable area actually lost its gas supply and needed to be reconnected?

In my house the combi should be fine. The sensor will detect no gas and close the valve off. I am sure my cooker would fill the house up with gas if it lost its gas supply and then was reconnected. The closest scenario I can find is when a gas main got filled with water in a nearby village (about 10 years ago) and each house on the supply had to be checked at the meter. That was over 200 houses and it took a few weeks before everyone was back to normal. I believe that every house had to be disconnected at the meter and connected back up one by one.

Adam

[Dave Liquorice]

Reading between the lines of the reports relating to the big gas main fire at Rawtenstall just before Christmas. They tell people to turn their gas off at the meter. They then pressurise the main again, presumably purging and checking for leaks as they say not turning off at the meter may slow down return of supply. After that they visit every property and check it, making sure pilot lights are lit etc.

A lot of ex-soviet Eastern Eurpean countries have massive communal heating systems, not just individual buildings but whole blocks and towns.

[Tim Downie]

That happened with us recently when a gas main was accidentally cut. Before the supply could be restored, every house ahd to have its gas supply turned off. Fine if you were in the house when they called. If not, they dug up your incoming supply and physically cut it off.

Tim

[Ed Sirett]

If someone chops through a service main with a JCB, it's much cheaper to let the gas vent and monitor the pressure than to cut the gas off.

[ARWadsworth]

I have had the pleasure of visiting some ex-soviet Eastern European countries. The "modern" tower blocks which could mean anything from 1970 onwards may well have the communal heating systems. Believe it or not there are systems in place that are quite similar in Doncaster. I was gobsmacked when I saw it.

Adam

[The Natural Philosopher]

Doncaster is pat of Eastern Europe ;-)

[Martin Bonner]

But you probably want to discourage people from welding the pipe back together again :-)

[Huge]

Oh, I don't see why not, given that modern gas mains are made of plastic. :o)