must i replace the gas pipe?

[bluesky]

recently i have updated a conventional boiler with a vaillant 831, the gas pipe is under floor and about 10m long, it looks ok so i did not replace the gas pipe, however after replacing the boiler i found that the inlet pressure is only 17mb, meter working pressure is 21mb, aothough the minimum requirement is only 16mb for vaillant and the boiler should work safely(flow rate is ok), the pressure drop is aoubt 4mb, must i replace the gas pipe under the floor boards? thanks all!

 

[AlexGas]

The problem is I do not know what is gong on under the tiled floor, maybe some 15mm pipe there, I assume the pressure drop is more than 1MB, but is it mandatory for me to update the existing gas pipe?if I install new pipe work surely I need to make sure the pressure drop is less than 1MB, My job was only to change the boiler and what I know is the boiler working fine

From current BS 6798:2009
Specification for installation and maintenance of gas-fired boilers of rated input not exceeding 70 kW net

5.5 Gas supplies and pipework
5.5.1 First and second family gases
5.5.1.1 The gas supply pressure to the boiler shall be controlled in accordance with the boiler manufacturer’s instructions.
5.5.1.2 Where a service pipe exists, the operative shall confirm with the gas supplier or public gas transporter that the pipe is of sufficient size for the maximum gas rate of the whole installation.
...

5.5.1.4 All gas installation pipes shall be sized and installed in
accordance with BS 6891 or IGEM/UP/2, Edition 2, as appropriate.

COMMENTARY AND RECOMMENDATIONS ON 5.5.1.4
When replacing an existing boiler and reusing the existing gas supply pipe, the operative should confirm that the pipe is of adequate size to supply the new boiler before fitting the boiler.

 

[Reltub]

There are a lot of restrictions in the vaillants i think they allow about 1.5mb for this so 2.5mb in total. Only way to be sure your gas is correctly sized is to fit a test point under the boiler. But as said you can't leave a new install with n.c.s on them.

IMO as long as the gas rate is ok and the inlet pressure is no more than 2.5mb difference at the gas valve i don't see an issue.

 

[tamz]

I don't think i've ever had a Vaillant running at more than 18.5 testing on the gas valve and that was sitting on top of the meter.
As said in post#2 if you want to check your pipework drop exactly cut a test point in below the boiler.

does that mean all the installer have to make sure the gas installation is perfect when they replace a boiler: like make sure the gas hob must have FSD? the meter must have bonding? open the floor boards to make sure all the pipes clipped ok? replace all the lead pipes(this one as i know it is not mandatory),etc..... then all the boiler replacement will be a big job

No but you have a duty to check all other appliances and notify any defects or non compliances.

 

[galaxy_plumbing]

do you have any accessible space where you can upgrade to 28/35mm to bump the pressure a bit?

 

[Billy Bob Bob]

recently i have updated a conventional boiler with a vaillant 831, the gas pipe is under floor and about 10m long, it looks ok so i did not replace the gas pipe, however after replacing the boiler i found that the inlet pressure is only 17mb, meter working pressure is 21mb, aothough the minimum requirement is only 16mb for vaillant and the boiler should work safely(flow rate is ok), the pressure drop is aoubt 4mb, must i replace the gas pipe under the floor boards? thanks all!

yes you must replace the pipe i dont really care what MI,S say,you are fitting it to GUISR,1mb drop max

 

[AlexGas]

From current BS 6891:2005

Installation of low pressure gas pipework of up to 35 mm (R1¼) in domestic premises (2nd family gas) — Specification

5.2 Pipe sizing
5.2.1 When designing an installation, the sizes of all installation pipes shall be determined from the maximum gas rate of the appliances to be connected.

COMMENTARY AND RECOMMENDATIONS ON 5.2.1
Allowance should also be made for any future extensions which might be anticipated, especially if the pipes are to be buried. Annex A gives a method of calculating pipe sizes in a system.

5.2.2 The pressure drop between the outlet of the meter and the points to be connected shall not exceed 1 mbar at maximum flow conditions (see Table 1).

 

[Reltub]

I think the inlet pressure technical bulletin covers this.

 

[jase158]

recently i have updated a conventional boiler with a vaillant 831, the gas pipe is under floor and about 10m long, it looks ok so i did not replace the gas pipe, however after replacing the boiler i found that the inlet pressure is only 17mb, meter working pressure is 21mb, aothough the minimum requirement is only 16mb for vaillant and the boiler should work safely(flow rate is ok), the pressure drop is aoubt 4mb, must i replace the gas pipe under the floor boards? thanks all!

A few things worry me here, working pressure at meter, standing pressure at boiler- 2 different things surely!! you need working pressure at boiler not standing pressure!! you say the pipework "looked ok" did you do TT?

 

[Reltub]

Where does it say standing pressure?
The way i read it as his inlet pressure is working

 

[kirkgas]

You seem to be trying to get out of doing the job correctly, however as already advised, fit a test point just before the pipe goes into the boiler and measure it there, and it might be ok, but at this stage it isn't good enough to now be checking pipes and pressure, it should have been done and priced before you started or noticed and rectified when you fully and properly commissioned the new appliance, do you know how to work out gas flow at appliance by calculating pipe size and run? Ok you can see what's under floor, but work on best practice, gas rate it and test pressure at pipe NOT after restriction on gas valve the. See what you get

 

[Reg Man]

Standing pressure at the boiler tells you nothing of importance. Its working pressure on the boiler inlet, under maximum flow with all appliances running which tells you the correct figure.

 

[Masood]

Fit one of these close to the boiler. That will give you your working pressure without the restriction from the boiler's gas valve. As already said, make sure other appliances are on full blast. No cheating by "forgetting" to turn them on!

GAS PRESSURE TEST EQUIPMENT