Burner pressures

[Gav e]

Hi guys!!

Just wanted to know if anyone can help me out, I am filling in my portfolio
and cannot get hold of my gas engineer for a week and a half (on holiday)

I am writing up 2 jobs we done last week and I am a little cconfused. We serviced a
vaillant ecotec pro24
standing pressure was 23mbar
Inlet pressure at appliance is 23mbar
working pressure at meter was 21mbar
Inlet working pressure was 18 mbar

I was Under the impression you was only aloud 1 mbar drop, even though mi states between
17-25mbar is ok
Can someone please help

Gav (first time poster)

 

[Simon F]

Hello Gav, welcome along.
standing pressure of 23mbar would be the same anywhere on the pipe work.
pipe work may well be undersized, you saw it, what was it like? what did your boss say?
was there any other appliances on the same pipe? that would be more of a concern if they were being starved of pressure when everything is running.

 

[Masood]

You are only allowed 1mbar drop in working pressure, but as long as the flame picture is OK and FGA readings within tolerances I'd class that as AR but not necessary to shut it down. I'm sure there will be different opinions on this! 🙂

 

[Gav e]

Hi thanks for your replys, the pipe work is in 22mm and only 5 meters so ok.

If you connect the manometer to test point one on the gas valve is this the working pressure?
Thank s

 

[Masood]

Hi thanks for your replys, the pipe work is in 22mm and only 5 meters so ok.

If you connect the manometer to test point one on the gas valve is this the working pressure?
Thank s

Well it's clearly not OK, as you have a 3mbar drop between meter and appliance! It's not just about length of pipe run...

The MIs will tell you which test point is which.

 

[Gav e]

Hi spoke to vaillant direct, they said you always go by the mi and the 1mbar drop
doesnt count if its in the mi tolerances. Mi states between 17 - 25 mbar
thanks for your input

 

[diamondgas]

... I'd class that as AR but not necessary to shut it down. I'm sure there will be different opinions on this! 🙂

I have a different opinion 🙂 NCS 🙂

If you AR then you're telling the customer they have something potentially dangerous in their home and you're advising them not to use it! Imagine the implications that could have on the original installer, your employer and the unneccessary expense IMO that the custard would have to undertake to increase the pipe size!

As long as the appliance is otherwise working correctly and is not significantly effecting the workings of other appliances then make a note of your findings via the NCS procedure!

 

[Masood]

I have a different opinion 🙂 NCS 🙂

If you AR then you're telling the customer they have something potentially dangerous in their home and you're advising them not to use it! Imagine the implications that could have on the original installer, your employer and the unneccessary expense IMO that the custard would have to undertake to increase the pipe size!

As long as the appliance is otherwise working correctly and is not significantly effecting the workings of other appliances then make a note of your findings via the NCS procedure!

I can see your point, and am certainly not going to argue! I tend to err on the side of being a little over-cautious perhaps! 🙂

 

[Masood]

Hi spoke to vaillant direct, they said you always go by the mi and the 1mbar drop
doesnt count if its in the mi tolerances. Mi states between 17 - 25 mbar
thanks for your input

No, that's not entirely accurate.

MI's take precedence when it comes to the appliance itself. They have no sway over the overall installation. Working pressure at the boiler, anywhere in the range 17-25mbar would be acceptable for boiler function (and warranty!), but the maximum 1mbar pressure drop between meter and appliance is a Gas Safe (and thus HSE) stipulation and cannot be superseded by MI's for the simple reason that the manufacturer cannot possibly allow for all the possible permutations of pipe length, diameter, bends, fitting and other appliances on the installation!

 

[Blumper]

The GIUSP state that : 'Undersized installations, which do not affect the safety of any appliance operation, or prevent any appliance(s) from operating at its minimum intended gas heat input rating, are normally clasified as NCS'...

BUT, it also states that the pressure drop across a gas carcass MUST NOT exceed 1mb....so everyone is right really, but I would also class it as NCS, providing all appliances are working ok...or cover your booty and class it as AR, the custard can always turn on the appliance as soon as your gone, its your, (or your engineers at least) call.

Another thing, if you were able to take the working pressure from a point just before the boiler connection, you might find your wp in the gas carcass is within tolerance, you don't know by how much the gas pressure is dropping from the connection to the boiler through the boilers internals to the test point on the gas valve... ? Worcester Bosch for example allow for upto 1.5mb drop from the gas connection to the test point on the valve (Greenstar's), giving you 2.5mb max wp drop from meter to gas valve test point.

And yes, if you take your reading from test point 1 while the boiler is running at max, that is your inlet working pressure.

 

[Millsy 82]

Vaillant do allow for a pressure drop across the gas valve I had 1 at 17mbar all working fine never affected the hob which worked fine when boiler on max. I spoke to Vaillant and I think it was the same as worcester of 1.5mbar drop across the gas valve.

The only way to test for sure is fit a test nipple on the gas before it enters the boiler.

 

[RPG 80]

Id be looking to make sure the gas rate and the co2 % meet the MI's

 

[Gav e]

Hi
sorry should of stated before, when the hob and oven is running on full boiler stays at 18mbar.
And hob and oven stay at 20.5 mbar with all appliances on full (0.5mbar drop which is ok)
co is 9.02 which is spot on a
nd ratio and Ppm was good to. Have not got the readings
as I am out.

 

[Gav e]

Thanks for your help, like you all said best thing is to fit test nipple before the boiler.

 

[diamondgas]

Gav e ... if you're writing up then mention that you've raised the issue with the manufactureres' and they stated the parameters and the boiler was within recommendations, you've done further research and realised that there's a recognised pressure drop possible across appliance inlet valves and components and without the necessary equipment was unable to test before the appliance so accept mi's and readings concur and the appliance is okay! 🙂 That'll get you a gold star :rofl: 🙂