Is there a danger if Operating/working pressure is below 18mb?

[Neddy1984]

Hi there,
Obviously pressure from the meter should be 21mb +/- 2mb, and you are allowed a drop of 1mb in pressure from the meter to the appliance, but many boilers i come across have operating/working pressures of 15,16,17, mb etc.
My question is even though the heat inputs are in line with the manufacturers instructions and the appliances are working fine, does this low pressure pose a threat either to the appliance or customer in the long run. And if so what can be done about it?
Or is this normal and i'm just getting confused between static/standing pressure and working pressure.
Thanks in advance.

 

[SimonJohns]

at what point are you measuring this?
what is the working at the meter?
is it a vallaint?

and yes there is if you ask GSR, it is said that the pressure drop can cause a flash back through pipe work, but i think the main reason is going to be that with the pressure not being a constant you cannot ensure correct combustion values and therefore possibly causing the appliance to be incorrectly gassed and producing CO and with more faults, e.g flueing or ventalation it could pose a severe risk to health

 

[gaspastemania]

What do the MI's say? I think some worcesters can read lower ,
If you use a u gauge check water level as had low readings then realised my water level was low ,,,,doh !!

 

[diamondgas]

My personal take has nothing to do with supply to the more moders condensing combi's with compensating governers, more their effect on the internal supply to other appliances ! There has to be a limit to the amount of pressure loss you can allow before there;s a chance of it becoming dangerous. I'd expect HSE lifted the recommended to them to a fail safe, no come-backs to us limit of 1mbar! IMO

 

[mickie]

normally when the working pressure is down the burner pressure will be too, but you can norally adjust the burner pressure to the M.I's but you should make sure then if its been working at the wrong pressure that its ratio, c.o. isnt too high, as heatexchangers tend to block up running the wrong burnerpressure.. if ratio is fine then its not dangerous..

you have to be sure its not dangerously affecting appliances if pressures are out with everything running together, if all appliances running together all check out ok with the anyliser, and the boiler doesnt make fires or cookers go out, you put it down as ncs

 

[Barry98]

What do the MI's say? I think some worcesters can read lower ,
If you use a u gauge check water level as had low readings then realised my water level was low ,,,,doh !!

havent we all , or the trainee on his first time opens the ecv fully and it all flys out of the end , i stick to mi V2 now adays

 

[GQuigley67]

speaking to the Transco guy the other day, he said that they dont use electronic Gauges becuse you would have to leave them beside the meter for 40 minutes if you were coming from a cold van into a warm house because of temperature differentials and the readings would be jumping up and down, and truth to this ??

 

[emerald]

i found a boiler dropping to 12 mbar at full rate, a valliant i think it was, i wasnt sure what to class it as (NCS, AR, ID) so i rang our trusted friends from corgi to ask what they thought, he just said what does the flame look like, is it wavering, or lifting or yellow. or is there any sign of destress.
my answer to all of these was none of the above, and his answer to that was ncs, leave it as it is and write it on your service record

 

[Billy Bob Bob]

My personal take has nothing to do with supply to the more moders condensing combi's with compensating governers, more their effect on the internal supply to other appliances ! There has to be a limit to the amount of pressure loss you can allow before there;s a chance of it becoming dangerous. I'd expect HSE lifted the recommended to them to a fail safe, no come-backs to us limit of 1mbar! IMO

exactly if you have a boiler that runs at 17 max rate and a gas hob with no ffd requiring 20 what is gonna happen when the hob gets staved of gas its not a case of the boiler being dangerous its the other appliances that will be affected

 

[Neddy1984]

I find this quite often too. thanks, great bit of info

 

[splinterdream]

i find that if you look at the gas isolation to the boiler they can often reduce the size of the inlet to as little as 10mm.

 

[AWheating]

some modern boilers will give you a lower reading at the inlet side of the gas valve due to pressure loss from iso valve to the inlet test point (this is caused by pipework,filters etc...). So you can sometimes have a drop of say 1-1.5mb due to this efect, which is why some boilers have a min inlet pressure of 18-19 mb and not 20mb.

i would personally like these boilers to have a test nipy fitted to iso valve to enable an engineer to confirm that this drop is due to internal appliance factors and not pipework, this would eliminate the unknown for the installers and not give a easy excuse.

there is a tech bulletin about this i believe.

 

[Surveyor5]

I am not sure what is being measured here, or from where. Working pressure is the pressure at the meter test point when there is an appliance running. In ideal circumstances this should be 21mb+-2 but may well be lower particularly at periods of peak demand. If working pressure at the meter is significantly lower than this, as described in the original question, this should be phoned thro to National Grid as the meter regulator is probably faulty.
As previously stated the loss between the meter and the appliance inlet should not exceed 1mb, if it does this would suggest undersized pipework or possibly a blockage. Burner pressures on older appliances will vary, but details should be in MI's or on the appliance data badge.

 

[SimonJohns]

I am not sure what is being measured here, or from where. Working pressure is the pressure at the meter test point when there is an appliance running. In ideal circumstances this should be 21mb+-2 but may well be lower particularly at periods of peak demand. If working pressure at the meter is significantly lower than this, as described in the original question, this should be phoned thro to National Grid as the meter regulator is probably faulty.
As previously stated the loss between the meter and the appliance inlet should not exceed 1mb, if it does this would suggest undersized pipework or possibly a blockage. Burner pressures on older appliances will vary, but details should be in MI's or on the appliance data badge.

Well on certain modern valliant boiler for example, the pressure read on the inlet to the gas valve. Will tend to read low even if the boiler is right next to gas meter and piped in 28mm. What we are saying is that this is a contravention and how can it be ok for a large corporation but not for the little men

Burner pressures arnt comin in to this regarding the pressure losses. But to bring them in as on previous posts. Is because of the pressure losses this would cause an adverse effect on the burner pressures


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[GQuigley67]

Vaillant allow up to 2.5mbar drop in their gas valves

 

[Pssst]

speaking to the Transco guy the other day, he said that they dont use electronic Gauges becuse you would have to leave them beside the meter for 40 minutes if you were coming from a cold van into a warm house because of temperature differentials and the readings would be jumping up and down, and truth to this ??

Load of tosh. IMHO there is no need to use an electronic guage for normal domestic work at low pressure. NG do not issue electronic guages for domestic work purely becuase they are not necessary and therefore it would be an un-necessary spend. Electronic guages are of course used to measure higher pressures where a water guage would of course be useless..!

 

[Steve @ TheHeatingHub]

Vaillant allow up to 2.5mbar drop in their gas valves

I do not wish to come across argumentative but in the nicest possible way where did you get this info GQ ? The reason I ask is I was having this exact discussion the other day and I said you are allowed only 1.5 through the gas valve + 1mb on the pipe work as Vaillant say the minimum you are allowed to the a 831 one is is 16.5mb officially (although I have heard they run fine at 14mb) which would be 1.5mb loss for the gas valve and 1mb loss for the pipe work if the wp at the meter was 19mb ofc would give you the bare minimum of 16.5

Would love to hear your thoughts on this