Vaillant boiler

[goz666]

Good afternoon GSR's have a problem i need to sort, may mean me asking a few questions to get my head round things as I might have miscalculated a boiler installation I did.

Fitting a 37kw boiler what would you calculate as the requirements for correct pipe size and Gas rate ??? Not looking at the manual as I did not have this until installation day ??

 

[diamondgas]

It'll depend on the length of run goz666 and how many appliances are fed from the supply. I'd imagine you'd need some 28mm somewhere in the equation 🙂

 

[goz666]

It'll depend on the length of run goz666 and how many appliances are fed from the supply. I'd imagine you'd need some 28mm somewhere in the equation 🙂

Total run is 8 metres + 6 fittings so 11 metres total....no other appliances in use, cooker is all electric. Meter is on outside wall about 5 metres away and the pipe goes in the house in 22mm up the inside wall (not visible) then up n over to boiler.

 

[diamondgas]

According to charts I have you can get 3.9m[SUP]3[/SUP]/hr at 12m of 22mm pipe ... 37kW=3.5m[SUP]3[/SUP]/hr thereabouts so 22mm from the meter should be adequate I'd say yeh? Are you getting a greater than 1mbar drop?

 

[goz666]

According to charts I have you can get 3.9m[SUP]3[/SUP]/hr at 12m of 22mm pipe ... 37kW=3.5m[SUP]3[/SUP]/hr thereabouts so 22mm from the meter should be adequate I'd say yeh? Are you getting a greater than 1mbar drop?

Thanks DG, that's exactly what I worked out at the time...had my inspection yesterday and he checked this boiler. Working Pressure at meter 21.0mb am getting 20mb at the gas valve inlet, the inspector put the boiler in full mode and said you've only got 14mb a drop of 6mb ?? couldn't understand why because I worked it out beforehand and when commissioning all was spot on. I did the gas rate and that was 3.3 m3/hr he said this was acceptable so I've been trying to contact Vaillant techs all day with no joy. Need to go back there and recheck everything because my workings out had me just in like yours so I'm lost whats happened in four months ??

 

[goz666]

Truth is mate, am thrashed to death thinking I may have got it wrong. I've worked this out about twenty times since yesterday and it's doing my nut in. Maybe I should leave it a few days then think about it again ..lol.

 

[diamondgas]

Have you checked the WP at the meter when the gas is at full rate, was that 21mbar? If you've got a drop that much I'd suspect a dodgy meter or some blockage got into the pipework somehow?

 

[stevetheplumber]

ive just had the same thing with a wb 37kw about 25ft equivalent length all in inch except the section behind the boiler definately no blockages and i was still losing 2mb across the system working at meter 19 at boiler 17gas rate right fga right i piped it in 22 first as i wasnt aware it was a 37kw boiler that sucked the life out of the hob

 

[goz666]

ive just had the same thing with a wb 37kw about 25ft equivalent length all in inch except the section behind the boiler definately no blockages and i was still losing 2mb across the system working at meter 19 at boiler 17gas rate right fga right i piped it in 22 first as i wasnt aware it was a 37kw boiler that sucked the life out of the hob

Well I'm gunna have to go back mate and do all these checks again for my own peace of mind and my customers. If the pipe is undersized I haven't a clue how I'm going to change it because it's an outside meter cupboard, front of the house and the pipe is buried behind the plasterboard internally and it would mean ripping their study apart to uprate the pipe.
If my original calculations would've been borderline, (and I also checked with my iphone app) I would've put a smaller boiler in.

 

[Nostrum]

ive just had the same thing with a wb 37kw about 25ft equivalent length all in inch except the section behind the boiler definately no blockages and i was still losing 2mb across the system working at meter 19 at boiler 17gas rate right fga right i piped it in 22 first as i wasnt aware it was a 37kw boiler that sucked the life out of the hob

Unless you cut a test point in under the boiler you'll always get at least a 1mb drop from the inlet tap to gas valve test point mate. Both worcester and vaillant say that you can expect up to a 2mb drop across the valve, plus your 1mb across pipework! Ideal have a little chart in the book which is comparable to the output.

 

[CES]

I agree with sambotc, Id cut in a test point in the gas pipe below the boiler and check it.

 

[Nostrum]

I'd also get the regulator adjusted if poss 21 mbar at the meter should get you nearer 19.5 at appliance. I'd be happy with that. I think worcester state minimum of 18.5 at the gas valve.

The reg's need updating if you ask me