Running several gas appliances together - low gas pressure

Discussion in 'Plumbers' Talk' started by Elisabeth Guyer, Oct 12, 2019.

  1. Elisabeth Guyer

    Elisabeth Guyer New Member

    I have recently replaced my very expensive to run, electrically heated water cylinder with a gas combi boiler recommended by my gas engineer which just supplies hot water. My central heating is supplied by a gas fired warm air system which I love and don't want to change.

    The combi-boiler has a rating of 35kw, the warm air unit 24kw and they are impossible to run together. Every time I switch on a hot tap it cuts out the pilot light on the warm air unit so no central heating.... I am now considering changing the combi-boiler for a multi-point water heater but am struggling to find a suitable model with a kw rating which is significantly less than the boiler. They mostly seem to be 24 - 30kw?

    I have been told by my Gas Network providers that I only have a 3 cubic metre supply (my gas installer assumed it was 6 cubic metres) despite having a 5 bed house. They want to install a bigger supply but it involves ripping up my driveway to do it and I can't afford to have it resurfaced.

    Any suggestions please?
  2. The Teach

    The Teach Screwfix Select

    hey,dont worry. The extinction rebellion crew want natural gas to be banned sooner than what our gov was planning.

    Maybe consider an alternative fuel for some of your heating requirement or ask your gas service technician to download their findings so something more practical can be temporally worked out.

    there will be some exposure to cost,your cost :(
    Elisabeth Guyer likes this.
  3. Peterdevon

    Peterdevon Active Member

    I think I would be asking the installer for my money back as it doesn't work.
  4. spirits are real 2016

    spirits are real 2016 Screwfix Select

    you could always have a new bigger pipe moled under the drive way without having to rip up the tarmac...
  5. ajohn

    ajohn Screwfix Select

    The gas meter probably is the problem. Not sure about the real need to rip up your drive though. We had 2 meters and switched to one but may go to separate central heating and hot water heating when our heating is upgraded. As we had 2 which I assume were 3cu m the supply should run a 6. I did discuss this with the supplier complaints dept and gained the impression that they would just fit a higher capacity one there and then if I wanted. :) Wish I had said yes now.

    Pipe work can cause problems as well. It needs to be a certain size and I would have thought 2 units like you mention would want separate pipes back to the meter or rather large pipe to where the 2 are joined. I'm left wondering why some one fitted a combi when all you need is water heating. Something smells in this area so I'd suggest you get some one who definitely is gas registered to take a look. Not sure how this works on gas but assume they are registered.

    Our property did have 2 under sink hot water heaters as 2 ladies owned the house and wanted separate bills. From memory they were about 10kw in modern units. Not sure if similar is still available. We used them for several years. Ok for baths, washing up and my first experience of a high pressure shower. Seems low to what people use these days so maybe more efficient for this use. They would have been fitted 40 to 50 years ago.

  6. Mike83

    Mike83 Screwfix Select

    To be honest your combi should be disconnected from the supply as there’s not enough gas/pressure to supply both.
    I would think 3 m3 would only cover the warm air unit,I don’t think it would cover the combi by itself.

    if the supply isn’t upgraded you can’t have 2 appliances connected to the supply.
  7. ajohn

    ajohn Screwfix Select

    Problem with the need as I see it - isn't the mains pressure higher than what comes out of the meter?

  8. spirits are real 2016

    spirits are real 2016 Screwfix Select

    I'm just wondering if you had a bigger pipe installed then you would get a bigger gas meter and higher pressure..
  9. Mike83

    Mike83 Screwfix Select

    The pressure is higher but the regulator reduces it.
    If the pipe is undersized from the street to the meter then this will need upgraded to supply more than the current 3 m3.
  10. ajohn

    ajohn Screwfix Select

    24kw + 35kw = 59

    59 / 38.5 = 1.532 L/sec
    1.532 * 3.6 = 5.52 M^3/hr

    24kw works out at 2.24 m^3 / hr

    35kw works out at 3.27 m^3/hr

    I'd want my money back as only specific people should do this work now and they shouldn't assume anything. As they did I would also wonder about correct pipe sizing.

    The Teach and Mike83 like this.
  11. ajohn

    ajohn Screwfix Select

    I'd suspect that the OP should get some one to check what size it actually is and it's capability. Privatisation is "wonderful" but it can also encourage certain areas to go for as much income as possible.

  12. Mike83

    Mike83 Screwfix Select

    The supply will supply over 3m3 but probably not quite 6m3.
    That’s possibly why the smaller meter has been fitted.
    But nothing the domestic guys can do as the gas supplier owns the meter/supply.
  13. Mike83

    Mike83 Screwfix Select

    The meter will match the supply usually.
    It’s then up to any installation to check the capacity of the meter before fitting any appliance.
  14. kiaora

    kiaora Screwfix Select

    My understanding is the minimum gas meter size is u6,
    There’s two issues here, it’s quite normal to assume the meter will provide 6 cu / m

    if the warm air pilot goes out when the hot water is turned on, it points to gas pipe sizing problems,
    if there is a problem with the supply, that needs addressing.

    the minimum you need for hot water flow of, say 10l p/m is 24 Kw

    To me. I would be inclined to check out the gas pipe sizes, as a priority.

    Good luck
  15. Mike83

    Mike83 Screwfix Select

    I would have been looking at the pipe sizing also but the op says the supplier has stipulated it’s a 3m3 supply/meter.
    So the pipe sizing could all be correctly calculated but it won’t matter.
    All a bit strange though.
    kiaora likes this.
  16. The Teach

    The Teach Screwfix Select

    Apart from the appliance's maximum outputs,some consideration of the 1mb pressure drop should be considered. Who knows without doing onsite testing,which may be satisfactory on that day :)

    theory & practice are a vast difference but just a guide for armchair dudes.
  17. Mike83

    Mike83 Screwfix Select

    Take a picture of the gas meter.
    We can then confirm it’s capacity
  18. Elisabeth Guyer

    Elisabeth Guyer New Member

    SGN have already tried to install a pipe this way and got their mole stuck under the driveway! (Still there) Having promised no damage to the drive when I agreed to the new supply, they then insisted they had to make 2 small holes for the drill which got stuck and now they want to run a channel all the way from kerbside to meter to put in a new pipe and get their drill back. The trouble is I'm already over the 3 cubic meter supply with my warm air unit and range cooker hob combined. (3.21) so any new gas appliance is going to overload it? I've attached some pics of the meter as suggested by Mike83 - it seems to indicate 6m supply but I have it in writing from SGN that its only 3m.

    Incidentally - is this reduced supply common knowledge? All the gas installers I have spoken to seem to assume a 6m supply as standard. If you work in the SGN region did you get any notification that it is now their standard practice to reduce supply to 3m? The original systems in the house (built in 1968) were the warm air central heating and a small gas heater heating a cylinder of water and my neighbour still has this set up and it works. I would prefer to have an instantaneous supply - are there any electric solutions here?

    Thanks for all the comments and suggestions

    Attached Files:

  19. Elisabeth Guyer

    Elisabeth Guyer New Member

    Effectively the warm air unit is not being used at all currently because it keeps going out, so no central heating. If I disconnect the combi there's no hot water and that's more important at the moment.
  20. Elisabeth Guyer

    Elisabeth Guyer New Member

    My gas installer calculated the demand for both appliances at under 6 cubic m. so he went ahead on this basis. The house was originally built in 1968 with separate gas appliances for heating and hot water. I don't mind having an upgraded supply but it will leave the drive looking a mess because SGN will only patch the channel they dig and I can't afford to resurface it so I'm trying to find other options before I go that route.

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