New boiler install with low gas pressure

[manbackh]

Hi. Just had a Worcester 30kw boiler fitted in the loft. Beforehand, the installer said something along the lines that according to his calculations the pressure would be on the border of acceptable, but he was happy to go ahead with the plan. Having install it, it appears to run fine but he says the gas pressure is 16mB when it should be 18mB. He says this should have no affect though and we don't need to worry about it.

Is he right? Sorting it will mean running a pipe up the outside of the house, meaning more work which someone will have to pay for. My concern is even if we're ok now we have no leeway for future reductions. Given this is a new (expensive) system I dont want to be storing up problems...

 

[dcawkwell]

The installation instructions will probably require 20mb pressure to the boiler a drop of 1mb from the meter. So you are giving the manufacturer a getout of their warranty should anything go wrong.

I would start by measuring the pressure at the gas meter as I often
find these are out and not giving the right pressure. If this is giving a low pressure it is possible to adjust it up to the maximum of the permissible range and therefore compensate for the loss in the pipework.

If may also be possible to just increase the first part of the pipework from say 22mm to 28mm piping to improve pressure without having to do the whole run.

I personally think the pressure isn't that important and within a couple of mb is ok. 16 is getting on the low side for correct operation.
At full power you won't be getting the maximum capacity of the boiler with only 16mb pressure.

 

[JBPHS]

This is a topical problem in the Combustion Chamber at the moment.

Personally, I do all calculations when pricing for work. If it is anywhere near borderline, I increase pipe size, etc. to be well within tolerances and include this in the price. Bear in mind, I usually fit 36kW boilers and adjust the parameters once installed. But I always fit gas pipework to allow for max heat input to boiler.

Check the Benchmark certificate in the back of the installation manual, this should be filled in as part of the commissioning, but as the pressure is low with all appliances operating at maximum rate, I doubt that this has been done correctly. I strongly advise to get this filled out to avoid sticky issues with regard to manufacturers warranty further down the line. The way I see it is that the appliance has not been fully commissioned, so should not be connected to the gas supply. But undersized gas pipework (if other tests are ok) is classed as Not to Current Standards. The engineer should have filled out a warning notice. The appliance can be still used if it's NCS. The gas pipe upgrade is required whether this was picked up before or after the install. Have a word with the installer to see what can be done.

James.

 

[Agile]

James is of course correct and that's what I do.

However, its a sad fact of life that customers go for the cheapest quote and exclude those who have added something for upgrading gas supply.

It will work correctly and the maximum heat output will not be reduced as the same volume of gas is being burnt.

However, the regulations require LESS than 1.0 mbar pressure loss on the supply pipe and your installer apparently has from 3-7 mbar loss.

To be so far out with his calculations makes me think that he well knew the pressure loss would be excessive! That is rather naughty to me!

Boiler makers usually ask for a minimum of 18 mbar at the connection point. Worcester are very user friendly and MIGHT raise no issues with this.

I expect that Gas Safe would not be happy though BUT as he did point it out to you at the outset so the cost of upgrading will be with you.

The boiler will work fine and this is a question of not meeting the laid down specifications for gas supplies!

Tony

 

[gas112]

Wrong dont forget worcester say allow 2.5mb of a drop for isolation valve and gas valve so that would take it to 18.5mb before the valve and may only be a 0.5mb drop

 

[manbackh]

Thanks for the replies guys. Bit unclear though as two of you say different things - will it affect max output or not? Given its getting less gas than recommended it would seem intuitive that it would. If so its more of an issue.

I made a mistake in not getting him at the start to clarify more clearly what the outcome would be if pressure *was* a problem. He seemed confident it was worth doing so I went along with it. Now I feel like I've been badly advised by him but he's not done anything I can demand he fixes. Live and learn...

 

[Agile]

Gas112 is commenting on the fact that some makers admit that there is a significant pressure loss inside their boiler before the internal test point.

The maximum 1.0 mbar pressure loss is between the meter and the connection onto the boiler !

The simple fact is we don't know what the gas meter pressure is in your case. How the installer measured or calculated the 16 mbar is also not known.

Without more facts we cannot usefully comment further!

Tony

 

[gas112]

That is known as Agile back tracking after a bit of thought

 

[manbackh]

I was more referring to dcawkwell saying it would affect max output and Tony saying it wouldn't. Can someone clear this up?

 

[Steelmasons]

The boiler utilizes a zero governor gas valve (premix) so don't concern yourself.

As gas112 said , an allowance must be made regarding pressure loss between isolation valve/inlet pressure test point , this can be in excess of 3mb for some appliances.

 

[Steelmasons]

Tony , the installer advised the client gas supply may be undersized before any work was undertaken , client pays for an upgrade period.

FWIW I always fit a test nipple at isso valve.

Too many try to put the blame on installer including fellow gas installers , been in this situation many a time.

 

[Steelmasons]

This is a topical problem in the Combustion Chamber at the moment.

James.

Congratulations James , please introduce yourself to the combustion chamber when you have the time.

Regards.......

 

[Dan Robinson]

Indeed the installer is in a damned if he does and damned if he doesn't on this one.

I know where my sympathies lie.

 

[Agile]

Tony , the installer advised the client gas supply may be undersized before any work was undertaken , client pays for an upgrade period.

I also said that the client has to pay in my post at 1542 today.

It is for the client to decide what to do it anything. Partial upgrading may be all that is needed.

But without further information on the pressures no one can advise further.

Tony

 

[Steelmasons]

However, the regulations require LESS than 1.0 mbar pressure loss on the supply pipe and your installer apparently has from 3-7 mbar loss.

To be so far out with his calculations makes me think that he well knew the pressure loss would be excessive! That is rather naughty to me.

Tony

Calculations would not be "far out" considering loss across gas train could be in the region of 2/3mb , if we bare this in mind then add 1mb for pressure loss across pipework from meter to appliance we get a working pressure at meter of around 20 mb.

I suggest you also bare this in mind before slating you're fellow rgi's in future.

Now if this were a vaillant 37kw then 15mb working pressure at appliance gas valve would be acceptable.