Low gas pressure

[Last Plumber]

Good luck

 

[jaydebruyne]

Didn't work! Got another 0.15 m3/h - now have to take up the floor to replace the rest of the run as the guy don't want it run externally..

 

[Scott_D]

have you cut a test point under the boiler?

 

[newcastle phill]

With the boiler on minimum rate does it still affect the hob ???.

 

[jaydebruyne]

have you cut a test point under the boiler?

No, plumbcenter didn't have any and I didn't have time to go elsewhere :/

 

[Simon F]

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.

no one else seems to be asking this so.
does the size change from 22 to 15 at some point under the floor?
how much 15mm pipe is there?
that will starve the flow dramatically!

 

[jaydebruyne]

no one else seems to be asking this so.
does the size change from 22 to 15 at some point under the floor?
how much 15mm pipe is there?
that will starve the flow dramatically!

It changes under the floor and no idea where.. so going to replace the rest of the run with 28 until it hits underneath the boiler which it'll then be 15 for about 500mm and tee off in 15 for the hob for about 1.5m

 

[Simon F]

sounds like that's the problem then,
run the 28 as far as practical then 22 straight to the boiler

 

[jaydebruyne]

sounds like that's the problem then,
run the 28 as far as practical then 22 straight to the boiler

Will be doing it Saturday. Cheers Simon

 

[Last Plumber]

no one else seems to be asking this so.
does the size change from 22 to 15 at some point under the floor?
how much 15mm pipe is there?
that will starve the flow dramatically!

I've asked about the 15mm!

I also asked about the hob and its burner setting!

I'd look at that before running 28mm

 

[Last Plumber]

no one else seems to be asking this so.
does the size change from 22 to 15 at some point under the floor?
how much 15mm pipe is there?
that will starve the flow dramatically!

I've asked about the 15mm!

I also asked about the hob and its burner setting!

I'd look at that before running 28mm

 

[jaydebruyne]

I've asked about the 15mm!

I also asked about the hob and its burner setting!

I'd look at that before running 28mm

You mentioned before about getting rid of the 15mm to the boiler, which the floor needs to come up for. So if we gonna take up the floor might as well complete the run to the boiler in 28. At least if they add any other appliances they'll be covered.

The hob is old. But I reckon once the run is all 28 and I detest it it'll be alright. Anyway, we'll see.

I need to get a hold of some test nipples to cut into the pipe under the appliances

 

[Scott_D]

Are you getting paid extra or was it part of the job?

 

[Last Plumber]

Yes ok.

Getting rid of that 15 will make all the difference.

Vaillant loose a good 2-3mb through the tube to the gas valve.
Whatever your wp is at the valve, it will be 2-3 Mb above that at the pipe below the boiler.

 

[jaydebruyne]

Yes ok.

Getting rid of that 15 will make all the difference.

Vaillant loose a good 2-3mb through the tube to the gas valve.
Whatever your wp is at the valve, it will be 2-3 Mb above that at the pipe below the boiler.

I can't believe it loses so much - I'm really not a fan of Vaillant

 

[Last Plumber]

I can't believe it loses so much - I'm really not a fan of Vaillant

I think they're one of the best around tbh
There are a few that are similar to be fair
Been installing commercials and domestic for ages and had no real probs.

 

[jaydebruyne]

Ok.. so I've done the entire run now in 28, dropped to 15 about 20cm under the boiler - it tees off about 10cm to the hob in 15. Boiler still only getting 2.85 m3h when min is 2.9. Hob still going out on simmer but I'm gonna replace the hob anyway as it's nearly 30 years old. Also gonna buy a test nipple for the 15mm under the boiler. Could it not be that the boiler is only demanding 2.85m3h - as it's rating at 30kW gross

 

[ShaunCorbs]

Ok.. so I've done the entire run now in 28, dropped to 15 about 20cm under the boiler - it tees off about 10cm to the hob in 15. Boiler still only getting 2.85 m3h when min is 2.9. Hob still going out on simmer but I'm gonna replace the hob anyway as it's nearly 30 years old. Also gonna buy a test nipple for the 15mm under the boiler. Could it not be that the boiler is only demanding 2.85m3h - as it's rating at 30kW gross

so the boilers in 15mm?

and whats pressure at boiler when hob is on improved?

 

[newcastle phill]

Have you teed the hob off the 28mm ? And hob now ok ?

I haven't read the whole lot again. But your allowed 10% below and 5% above rated figures.
And what model was it

 

[jaydebruyne]

so the boilers in 15mm?

and whats pressure at boiler when hob is on improved?

The total 15mm run is 20cm but yeah boiler is in 15. Didn't test boiler once reconnected hob as tested boiler with hob disconnected and was still slightly low. It's peeing me off. But am getting 21.5mbar at meter working pressure and 16 at boiler inlet on valve. Need to buy a test nipple. It's a new run so can't be a blockage.

 

[jaydebruyne]

Have you teed the hob off the 28mm ? And hob now ok ?

I haven't read the whole lot again. But your allowed 10% below and 5% above rated figures.
And what model was it

No ive kept the original tee there so hob is teed off Boiler about 10cm upstream from where 28mm reduces to 15. Boiler is a Vaillant ecotec Plus 630 - the minimum rated flow is 2.9m3h which is the -5% figure - nominal is 3m3h.

 

[ShaunCorbs]

The total 15mm run is 20cm but yeah boiler is in 15. Didn't test boiler once reconnected hob as tested boiler with hob disconnected and was still slightly low. It's peeing me off. But am getting 21.5mbar at meter working pressure and 16 at boiler inlet on valve. Need to buy a test nipple. It's a new run so can't be a blockage.

Isn't boiler gas in 22mm ??

 

[jaydebruyne]

Isn't boiler gas in 22mm ??

Nope.. 15 already sticking out the boiler from the box.. just gotta connect the 15mm iso and connect to gas.. :/

I've over compensated with my calculation and 28 is more than enough to feed 3.75m3h. Also, why would they put a 15mm gas connection in a 30kW boiler? Hate Vaillant!

 

[Scott_D]

Have you obsereved the pressure as the boiler fires up?
does it ever go below 16mb

 

[jaydebruyne]

Have you obsereved the pressure as the boiler fires up?
does it ever go below 16mb

I didn't, no. I put it on max rate and tested it after 5 mins and then again at 10 mins

 

[newcastle phill]

You can have as low as 17mb at the gas valve test point on that what includes gas valve losses, also they can gas rate at 2.91m ph and be perfecly within spec

 

[jaydebruyne]

You can have as low as 17mb at the gas valve test point on that what includes gas valve losses, also they can gas rate at 2.91m ph and be perfecly within spec

But I'm getting lower readings than this - 16mb and 2.85m3/h ??

 

[jaydebruyne]

The most I'm ever gonna get from that small section of 15mm is 2.9m3/h - anything higher needs 22mm - why would Vaillant ship a 30kW boiler that needs a nominal flow of 3m3/h with a 15mm connection??? Or am I missing something here (wouldn't be the first time!!)

 

[ShaunCorbs]

i would confirm you have require pressure below boiler and check hob is ok and leave it

its got 28mm to it ffs

its down to the bunny to up there inlets

 

[newcastle phill]

The most I'm ever gonna get from that small section of 15mm is 2.9m3/h - anything higher needs 22mm

Nope your looking at the tables wrong. That 2.9m3 refers to a 3m length of 15mm with a 1mb drop.
A mere 20 cm section would flow alot more than that...by my loose reckoning easily in excess of 5m3

 

[jaydebruyne]

Nope your looking at the tables wrong. That 2.9m3 refers to a 3m length of 15mm with a 1mb drop.
A mere 20 cm section would flow alot more than that...by my loose reckoning easily in excess of 5m3

I wasn't looking at a table. I was using the mr combi pipe size app and for the length of 15 I have with 1 elbow you won't get higher, needs to be 22

 

[mfgs]

Why not put a reducer on the connection from the boiler and take it straight to 22 or 28? That's what I do with boilers which have 15mm connections. I would also tee the hob off either the 22 or 28mm pipe.

 

[joni os]

App. and Tables in agreement 2.9 flow gives 3 meters and 20 meters for 15 &22.
Length 700mm pressure drop 700/3000 & 700/20000 which equates to the 0.233 & 0.035 given by App.
Phil also right with flow through 700mm length of 15mm. 1/4 of 3 meter length could be expected to give double the 3 meter flow, ( L X Q X Q approx constant).

 

[jaydebruyne]

App. and Tables in agreement 2.9 flow gives 3 meters and 20 meters for 15 &22.
Length 700mm pressure drop 700/3000 & 700/20000 which equates to the 0.233 & 0.035 given by App.
Phil also right with flow through 700mm length of 15mm. 1/4 of 3 meter length could be expected to give double the 3 meter flow, ( L X Q X Q approx constant).

Why does the app say for 2.91 with an effective length of 700mm you need 22?

 

[jaydebruyne]

Why not put a reducer on the connection from the boiler and take it straight to 22 or 28? That's what I do with boilers which have 15mm connections. I would also tee the hob off either the 22 or 28mm pipe.

I will do from now on! But from what Phil and Joni say I should get enough flow from that short run of 15 ... so what gives?