Currently reading:
Adding 3 metres of 28mm pipe at the end of a 15 metre 22mm run

Discuss Adding 3 metres of 28mm pipe at the end of a 15 metre 22mm run in the Plumbing Jobs | The Job-board area at PlumbersForums.net

Status
Not open for further replies.
B

boilerwoes

All,

First time poster, long time reader!

I need some advice before I get some quotes to resolve an issue. I found out a couple of days ago (from a boiler engineer) that the gas inlet working pressure at my boiler is too low (approx 13.5mbar). I haven't got precise figures, but apparently the working pressure at the gas meter is approximately 20mbar, but the boiler engineer was not precise about it. The system is gas tight, so no leaks. System has 22mm pipe to a boiler and to a gas hob. The 22mm reduces to 15mm for the last 0.5m for the boiler, and 1m for the gas hob.

Replacing the 22mm pipe with 28mm pipe from the gas meter is going to be hard due to obstacles etc. One option could be to increase the pipe size for the last 2-3 metres of the 22mm run, just before it enters the boiler, but am not sure if this will help reduce the pressure drop?

In terms of length of 22mm pipe - there is approx 15 metres of 22mm pipe between gas meter and boiler with about 10 corners and 1 tee. From the tee, there is approximately 3 metres of 22mm pipe before reducing down to 1 metre of 15mm pipe going into a hob.

Thanks in advance.
 
have your boiler gas rated and the inlet pressure checked on the hob, if the gas rate on the boiler and pressure drop on the hob are within limits leave the pipework as it is, the installation would be classed as NCS.
 
6mbar drop has nothing to do with the gas board, its your installation your engineer should sort thisyou may need more 28mm than the last 2-3m aswell
Understood. Just responding to fuzzy's post (look at the text i quoted) about the governor. I think recent changes to the system as part of a recent period of building works have resulted in a both job (we eventually kicked out the builders) so am left o pick up the pieces. I have an RGI coming to look at it but wanted to make sure I did some research first. The reality is that it will be tough to replace anything other than the last 2-3m with 28mm pipe. Perhaps a middle section of about 3m could also be replaced but that is about it without having to dig up walls (which you can understand I would like to avoid). This gives 5-6m of 28mm upgraded from 22mm (but not starting at the meter). But it generally sounds like upgrading sections of pipe to 28mm will help even if in the middle and end of the run (although a number of you have disagreed with that, so how do I convince my RGI if he disagrees as well).
 
Is this a new boiler install ?
No, been there a couple of years and pressure drop was fine before building work. Recent building work re routed a pipe and I asked them to ensure it was 22mm rather than the original 15mm for part of it. It is possible the measurement at the boiler taken by a boiler engineer a couple of weeks ago was incorrect so it may not be a 6mbar drop, but either way, the drop is high! I just dont understand how they could have introduced a big drop as essentially run is similar to before. Either way the builders are not coming back as I kicked them out for other shoddy work so they won't be solving it. Am hopeful that only sections can be replaced to fix the problem.
 
so who re-routed the pipework ?
It was all part of the building work (so the builders who i kicked out) so they would have contracted someone I think. Don't have the details of the actual person who did it so can't get him back to sort it. The original pipes were put in by another company.
 
you can buy a 15m tracpipe rerun for about £240, might be easier to rerun the whole gas carcass than fart about putting bits in.
Only problem is that it will either involve digging walls in addition to lifting floor boards (we would need to lift some floor boards in any case for upgrading sections to 28mm) so would rather not look at this option unless absolutely necessary
 
I don't know - just trying to summarise the points from the posts. Looks like the later posts say that increasing pipe size anywhere will increase volume, decrease resistance and increase working pressure at the appliance. The issue I am facing is that the pressure drop from gas meter to boiler is too great (around 6mbar) so am trying to determine ways of reducing this pressure drop. I am assuming the gas supply people won't change the governor to increase the gas meter pressure to above 22mbar?

increasing the pressure at the govener would not alter the drop in pressure across the system, they wouldnt do it anyway. you could do some pipe size calcs and work it out, normally its just a case of upsizing. Have you checked youve not got the manometer on the wrong size of the appliance have you and getting burner pressure? wouldnt be the first time somebody done that
 
increasing the pressure at the govener would not alter the drop in pressure across the system, they wouldnt do it anyway. you could do some pipe size calcs and work it out, normally its just a case of upsizing. Have you checked youve not got the manometer on the wrong size of the appliance have you and getting burner pressure? wouldnt be the first time somebody done that

The vaillant ecotec has a zero pressure govenor so no burner pressure to check.
 
The vaillant ecotec has a zero pressure govenor so no burner pressure to check.
Not sure I follow. What pressure would they have checked at the boiler then? He seemed to connect a manometer to something in the boiler. Would this be the pressure of the gas just before it hits the burner?Is anyone able to run a quick calculation to see what improvement I get in terms of pressure drop if I swap 5m of 22mm pipe with 5m of 28mm pipe?
 
how much gas m3/hr does the boiler use ?

edit: I see its a 31kw boiler so 2.79 m3/hr I will go and get my sizing table and have a look
 
Last edited:
not much at all your only losing 0.25mbar through that amount of pipework in 22mm you have to factor in bends and Tees aswell to get the total length

5m 22 = 0.25mbar
5m 28 = 0.16mbar
 
Ignoring the hob.

The pressure drop you have is down to more than you are stating.
A 15m x 22mm run with 10 elbows to the tee
then
3m x 22mm + 1m x 15mm + 1 elbow from tee would give an overall drop of around 1.68mb (it would be around 2.34mb allowing for a 7kw hob)

The 15mm part somewhere under the floor has never been upgraded. Get it done again and done right this time.
 
dont forget with a vailant you can lose 2mb wk press through the inlet elbow to the test point this is in the manual. i fitted a a large kw glowworm flexicom a while back and used a rear piping jig which only allowed 15mm pipe to the boiler from the top that reduced the wk press i cut a tee in and fitted test point on the 22mm part and got 20mb wk there .

ant
 
dont forget with a vailant you can lose 2mb wk press through the inlet elbow to the test point this is in the manual. i fitted a a large kw glowworm flexicom a while back and used a rear piping jig which only allowed 15mm pipe to the boiler from the top that reduced the wk press i cut a tee in and fitted test point on the 22mm part and got 20mb wk there .

ant

true indeed I was told at one of their courses that they allow 2.5mbar to be lost at inlet
 
increasing the working pressure at the meters govner will increase the working pressure at the boiler, who ever said it wont is wrong because while the gas board was out i got him to up it a little while he was upgrading it, which did help a lot
 
Ignoring the hob.

The pressure drop you have is down to more than you are stating.
A 15m x 22mm run with 10 elbows to the tee
then
3m x 22mm + 1m x 15mm + 1 elbow from tee would give an overall drop of around 1.68mb (it would be around 2.34mb allowing for a 7kw hob)

The 15mm part somewhere under the floor has never been upgraded. Get it done again and done right this time.

Thanks for the calculations. I do think it is a bit odd as before the building work, the working pressure at the boiler was 19mbar, so they must have screwed something up, but what? I am pretty sure 22mm pipe was added to the run for the hob (as the 22mm pipe was tee-d off the pipework going to the boiler). But I am wondering whether there is a blockage in the system. Maybe something is in the pipework that could be causing this significant pressure drop? Are there standard ways of flushing out debris, etc from gas pipework?

I guess the worse case scenario is to re-lay pipes etc, and I will need to have a think as to whether I want them in the walls or under the floors.
 
increasing the working pressure at the meters govner will increase the working pressure at the boiler, who ever said it wont is wrong because while the gas board was out i got him to up it a little while he was upgrading it, which did help a lot

Is there a maximum working pressure at the meters governer that the gas board will allow? I am wondering whether to ask them to increase the pressure (if possible) and then resign myself to the fact that there is a large pressure drop, but at least the working pressure at the appliances are higher? Thoughts on this approach?
 
it would yes but the pressure drop would still be the same

I am assuming you are referring to my question about the gas board increasing the pressure at the governor. In terms of the pressure drop being the same, I could live with that as long as the pressure to the appliances is high enough. So my next question is whether having a large pressure drop in the system is allowable as long as the appliances have their minimum required working pressure?
 
the working pressure is their to make sure a hob or another gas appliance doesnt go out while a boiler is running, also most boilers wont work properly with a working pressure of say, 15mb..

if you only have a boiler and nothing else, and the burner pressure is spot on, just the working pressure is down its only ncs, it wouldnt be dangerous.
 
I am assuming you are referring to my question about the gas board increasing the pressure at the governor. In terms of the pressure drop being the same, I could live with that as long as the pressure to the appliances is high enough. So my next question is whether having a large pressure drop in the system is allowable as long as the appliances have their minimum required working pressure?

doesnt matter if you can live with it or not, there should be no more than a 1mb drop across the system. there are reasons why the working pressures are controlled at the meter governor, if not you could run it in 10mm and just boost the pressure, but then its not safe
 
The minimum that vaillant allow is 17mb, I would disconnect the boiler and hob and blast some compressed air through the pipes, as the pipes have been cut to install a tee for the hob the installers may have got dirt ect in the pipe.
 
doesnt matter if you can live with it or not, there should be no more than a 1mb drop across the system. there are reasons why the working pressures are controlled at the meter governor, if not you could run it in 10mm and just boost the pressure, but then its not safe

Thanks Fuzzy - that's why I asked the question as I wasn't sure if there are regulations that state it can't be more than 1mb or not. Sounds like you are saying that there are regulations that state there cannot be more than a 1mb drop, full stop. So even if they were to up the pressure at the governor (to say 25mb), to allow about 19mb at both appliances, there would still be a "breach" of the regulations as the drop is 6mb.

So it sounds like the only option I have is to fix the fact that there is a 6mb drop across the pipework (either find source of blockage or re-lay new pipe), and reduce that to no more than 1-2mb. Is that right?
 
Status
Not open for further replies.

Reply to Adding 3 metres of 28mm pipe at the end of a 15 metre 22mm run in the Plumbing Jobs | The Job-board area at PlumbersForums.net

Back
Top
AdBlock Detected

We get it, advertisements are annoying!

Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website. For the best site experience please disable your AdBlocker.

I've Disabled AdBlock