Low gas pressure

[jaydebruyne]

Just finished commissioning the Vaillant boiler. Pressure slightly low at 2.76 m3/h. 30kW. Old boiler was a 24kW.

Tested the hob and all burners go out on simmer. Owners reckon this is a new thing.

Only hob and boiler on gas.

Pipework from meter is 22mm, goes in house and under floor in 22mm approx 3-3.5m. Comes out of floor where boiler is in 15mm.

Standing pressure 24mbar
Working pressure 21.5mbar

Undersized pipework I'm thinking.

Right or wrong??

 

[Riley]

How far is the run to the hob? Meter to first tee, tee to to boiler, then tee to hob. Any other appliances??

 

[Riley]

Gas rate of 2.76 is nearly spot on for a gross 30kw appliance?

 

[jaydebruyne]

Gas rate of 2.76 is nearly spot on for a gross 30kw appliance?

Min as per mi is 2.9.. hob tees off under the boiler which is about 2 meters away

 

[Riley]

Doesn't sound undersized to me for that distance.

 

[jaydebruyne]

Doesn't sound undersized to me for that distance.

What could be the issue then?

 

[ShaunCorbs]

whats pressure at meter working and then at boiler (full rate) no more than 1.5mbar drop if more its pipework / blockage

 

[wattsie1987]

As above what's your working inlet?

 

[jaydebruyne]

whats pressure at meter working and then at boiler (full rate) no more than 1.5mbar drop if more its pipework / blockage

21.5 working 16 at boiler inlet. Def pipework. Have disconnected hob and put boiler at risk. Am thinking of running the external 22 pipe in 28.. about 2 meters.

 

[ne1ls0n]

Black dust in gas line?

 

[ShaunCorbs]

21.5 working 16 at boiler inlet. Def pipework. Have disconnected hob and put boiler at risk. Am thinking of running the external 22 pipe in 28.. about 2 meters.

theres your problem new gas line

 

[jaydebruyne]

theres your problem new gas line

You reckon I could get away with upping the accessible 22mm to 28mm - about 2 meters

 

[ShaunCorbs]

You reckon I could get away with upping the accessible 22mm to 28mm - about 2 meters

depends if theres a blockage in the floor, as 22mm should be enough

as 30kw at 5m with 8 elbows gives you a loss of 0.60 mabar

the boiler inlet gas valve filter isnt blocked is it?

 

[kozak1968]

Maybe try using a compressor to blow any obstruction out first.

 

[jaydebruyne]

depends if theres a blockage in the floor, as 22mm should be enough

as 30kw at 5m with 8 elbows gives you a loss of 0.60 mabar

the boiler inlet gas valve filter isnt blocked is it?

Shouldn't be its a brand new boiler. Apparently hob was working fine before the install. But soon as I removed the meter I capped it and pipework with dust caps. Soon as I cut the gas under boiler I capped the pipe so nothing could drop into it.

I'll have the check the gas ISO valve make sure I didn't put it wrong way round, but that would only affect the boiler anyway.

 

[ShaunCorbs]

Shouldn't be its a brand new boiler. Apparently hob was working fine before the install. But soon as I removed the meter I capped it and pipework with dust caps. Soon as I cut the gas under boiler I capped the pipe so nothing could drop into it.

I'll have the check the gas ISO valve make sure I didn't put it wrong way round, but that would only affect the boiler anyway.

i would pull the gas valve just to check mesh

other than it being 15mm in the floor should be under 1.5mbar drop

 

[jaydebruyne]

i would pull the gas valve just to check mesh

other than it being 15mm in the floor should be under 1.5mbar drop

Gutted was gonna use this as part of my Inspection .. oh well

I'll pop round tomorrow and have a look at the gas valve.

Cheers Shaun

 

[jaydebruyne]

Maybe try using a compressor to blow any obstruction out first.

Don't have a compressor. Can you recommend one?

 

[joni os]

How many Kw is the hob?

 

[jaydebruyne]

How many Kw is the hob?

7, standard 4 burner

 

[Leo21]

Someone may have already asked this, what's the working pressure at the meter with all apliances running?
Does it alter when the the boilers on and then the hob? Becaouse it sounds like regulator to me.

 

[Leo21]

Someone may have already asked this, what's the working pressure at the meter with all apliances running?
Does it alter when the the boilers on and then the hob? Becaouse it sounds like regulator to me.

 

[jaydebruyne]

Someone may have already asked this, what's the working pressure at the meter with all apliances running?
Does it alter when the the boilers on and then the hob? Becaouse it sounds like regulator to me.

Tested and 21.5 when both are on, 21.5 when one appliance is on

 

[Last Plumber]

Get rid of the 15 mm to boiler and increase the min burner rate at hob ?
Or have I miss understood your post.

Apologies if I have, its late on a Sunday !

 

[Leo21]

Can you cut a tee with a test nipple on to the hob, and then look? Might be a restriction in the hob or isolater.

 

[wattsie1987]

Where are you testing the pressure at the boiler? If the gas valve Vaillant say upto 3.5 mb can be lost from boiler iso to gas valve test point. I alway fit one right under boiler so I know exactly what my pipe is loosing.

 

[jaydebruyne]

Where are you testing the pressure at the boiler? If the gas valve Vaillant say upto 3.5 mb can be lost from boiler iso to gas valve test point. I alway fit one right under boiler so I know exactly what my pipe is loosing.

Still doesn't account for 1mb drop.. 5.5mbar it dropped in total.. so 1 from meter to boiler, 3.5 from ISO at boiler to inlet on gas valve leaves another 1mbar unaccounted for

 

[Leo21]

Still doesn't account for 1mb drop.. 5.5mbar it dropped in total.. so 1 from meter to boiler, 3.5 from ISO at boiler to inlet on gas valve leaves another 1mbar unaccounted for

Have you checked your pockets?

 

[Leo21]

Still doesn't account for 1mb drop.. 5.5mbar it dropped in total.. so 1 from meter to boiler, 3.5 from ISO at boiler to inlet on gas valve leaves another 1mbar unaccounted for

Have you checked your pockets?

 

[jaydebruyne]

Have you checked your pockets?

Damnit, it's in there too! Lol

 

[wattsie1987]

Still doesn't account for 1mb drop.. 5.5mbar it dropped in total.. so 1 from meter to boiler, 3.5 from ISO at boiler to inlet on gas valve leaves another 1mbar unaccounted for

No but your pipework may not be loosing as much as you initially thought.

 

[wattsie1987]

Still doesn't account for 1mb drop.. 5.5mbar it dropped in total.. so 1 from meter to boiler, 3.5 from ISO at boiler to inlet on gas valve leaves another 1mbar unaccounted for

No but your pipework may not be loosing as much as you initially thought.

 

[jaydebruyne]

No but your pipework may not be loosing as much as you initially thought.

Very true. Dunno wether to blast pipework with a compressor to try clear any blockages or just do a new run. Going round tomorrow to check the gas valve and ISO valve. Will see what they say.

 

[ShaunCorbs]

Where are you testing the pressure at the boiler? If the gas valve Vaillant say upto 3.5 mb can be lost from boiler iso to gas valve test point. I alway fit one right under boiler so I know exactly what my pipe is loosing.

sorry but i disagree the hob wouldnt be going out due to 1 mbar, also ive never found anything near what mis say for gas valve restriction normally around 0.5-1 mbar

 

[Scott_D]

Slow reacting regulator when the boiler fires up?