reading gas pressure

[gaspastemania]

Can someone clarify few bits bobs for me .
As far as i am aware you allowed a pressure reading of plus or minus 1 from meter to appliance say boiler .If on my u gauge i get a reading of of more than this say a drop of 3 mbar to appliance from meter , would that indicate a blockage in gas pipe or faulty gas valve ?
Also on modulating gas valves what is the permissable drop ?
Am aware that some models could be different but is there a set rule ??

 

[mikegas]

your allowed 1mbar drop max from meter to appliance inlet, if you are getting more than 1mbar then there is either a blockage in the pipe work or more likely the pipe work is undersized. Some boilers allow more of a drop due to internal restrictions before the test point

 

[gaspastemania]

Thats what i thought your allowed a 1 mbar drop ,but had one today that was 2 mbar under and pipe work was 22mm to boiler and meter was close by . Also its older boiler which gas pipe undersized surely would have been picked up on earlier cp12's ( its a housing association appliance). Gas rate showed slightly under KW, but how would a blockage happen when no work has been done ???
Also modulating gas valves whats the lowest they can go??

 

[mikegas]

As its an existing appliance as long as the boiler is getting minimum burner pressure while all other appliances are on then the previous engineers can just class it as ncs, as for how blockages can be created maybe a filter blocked after works been carried out in the street not sure really somebody with more experience than me might know

low inlet pressure allowances has nothing to do with whether the boiler has a modulating gas valve or not. I think worcester allow as little as 16mbar on one of their boilers

 

[stevetheplumber]

there will be a minimun gas preasure for the modureg in the M I'S along with instructions to reset it if necessary it will be different for each boiler

 

[mikegas]

there will be a minimun gas preasure for the modureg in the M I'S along with instructions to reset it if necessary it will be different for each boiler

you mean for burner pressure though not inlet/working pressure

 

[kirkgas]

Can someone clarify few bits bobs for me .
As far as i am aware you allowed a pressure reading of plus or minus 1 from meter to appliance say boiler .If on my u gauge i get a reading of of more than this say a drop of 3 mbar to appliance from meter , would that indicate a blockage in gas pipe or faulty gas valve ?
Also on modulating gas valves what is the permissable drop ?
Am aware that some models could be different but is there a set rule ??

you are mixing up some terminology, plus or minus pressure is for standing pressure at the meter (21 + or - 2) you cannot have a plus pressure at the appliance, (ie 18 at the meter and then 19 at the appliance) a drop of more than 1mb could be down to undersized and or too long a pipe route and or too many bends, or as you say a blockage, it is unlikely to be a faulty gas valve (if you are measuring at the inlet side) faulty burner pressure could be down to a faulty valve, i admire your faith in previous CP1's :-( i'm not really sure what you mean by permissable drop on modulating gas valve, (could you be thinking of absorbtion through the gas valve which across some valves can be a few mb?) best way to confirm actual gas pressure is to fit a test point at the end of the gas pipe before it enters the appliance as this will measure "pipe" pressure rather than at the valve

 

[gasmarc]

i would have thought it was impossible to get a reading higher at the appliance than at the meter, I never stop learning in this trade lol

 

[gaspastemania]

I am aware meter readings are 19 - 23 mbar , But had a reading to at appliance of 18 mbar and meter rfeading was 21 mbar which is below the permissable allowance from what i am aware of .Pipe run was probably 3 meters with from what i could see not alot of elbows .Was a brittony 100 combi if memory is correct , what i cant get head around if it is pipework ( which i am sure it isnt) why has it never been picked up previous which why i dont think its pipework . If its blockage then how did that happen ????
The modulating gas valves was mentioned to me other week from an engineer ( who probably doesnt know much) said the condensing boilers can have lower readings at the appliance due to modulating gas valves.

 

[kirkgas]

next job would be to gas rate it to see what you get, not 100% sure but could it be possible the meter reg isnt working properly? thinking that if you get 21 at the meter but only 18 at the appliance is it opening properly to allow the gas to flow, as i said after checking pressure i would gas rate then take it from there

 

[rudeboytee]

I was speaking to the gas safe inspector recently and he told me that different manufacturers allow drops due to the restriction of the gas valve. For example baxi allow 1mbar for the gas valve so you would be allowed a total of 2mbar drop, 1 for pipework and 1 for gas valve. I believe that valliant allow 2mbar for gas valve so for one of them you would be allowed up to a 3mbar drop.

 

[gasmarc]

bosch allow 1.5 bar for gas valve apparently

 

[Alex Pelton]

could be a faulty governor. call transco and get them to change it. tell them u had low working pressure at the metre they class it as a gas emergency and change it within a couple of hours ( i think at least 4). bet this solves your 2 mb drop.

 

[arran197]

I went to a Baxi Duo Tec and the inlet would drop to 10mb when trying to fire up. The meter oulet would be the same, but it would fluctuate lots. Got Transco to change the gov and it was fine.