low inlet pressure

[mfgs]

I got called out to a worcester bosch greenstar 37cdi combi the other day. Locking out, flashing EA. Put the u gauge on, fire it up on max rate the inlet pressure was dropping to 0mb and locking out. Test at meter and got 20mb as it ramped up to max rate before locking out. Took the gas valve out and the filter was full of swarf from old barrel pipe but the whole outlet side of the meter is copper. I cleaned it all out, blew some gas through the open ended pipe and more swarf shot out. Put the valve back in, tested again. Now getting 2mb at max rate and still locking out. Out comes the gas valve again, filter blocked up again. Cleaned it out, blew more gas through the open pipe. Put back together, now getting 3.5mb at full rate and locking out. Take it out again, filter not too bad but clean anyway. put back together and now getting 6mb on max rate and the boiler isnt locking out remarkably.

I dont really know what to do, I have a feeling the gas valve has been damaged and is a bit blocked internally past the filter still as the last time it came out there was hardly any swarf. Will the gas transporter do anything about the main bringing in a load of crap? Do I just replace the gas valve? Or do I replace it and run a new supply from the meter incase there is any blockage of swarf along the way which is causing the low pressure?

 

[dave1]

What a bout removing meter outlet and give it a little blast and see if any comes through at the meter that way it'll prove whether its coming from the main or your side of meter.

 

[lame plumber]

May talking out my rear, but I'd talk to gas transporter, sounds like they may have worked on the line recently and disturbed/added all the muck. try dropping the meter box and blowing it through to clear any crud as well as blowing through the supplyline to the appliances first with a compressor and airline. then check pressures to see if you meet regs on the supply pipework, or if there is still a blockage new supply line needed. then look to replace gas valve, after all you need a proper supply before you blame the gas valve

 

[lame plumber]

What a bout removing meter outlet and give it a little blast and see if any comes through at the meter that way it'll prove whether its coming from the main or your side of meter.

ha beat me to it whilst Iwas learning to type

 

[mfgs]

What a bout removing meter outlet and give it a little blast and see if any comes through at the meter that way it'll prove whether its coming from the main or your side of meter.

The whole outlet side is copper, so it has to be coming from the main. I will disconnect the meter and blow it through to see what come out. I cant imagine the gas transporter will do anything though even if it is coming from their main?

 

[dave1]

The whole outlet side is copper, so it has to be coming from the main. I will disconnect the meter and blow it through to see what come out. I cant imagine the gas transporter will do anything though even if it is coming from their main?

Surely they'd have to if its affecting the appliances, it would at least be worth ringing them.

 

[Nostrum]

cut in a test point under the boiler and check max working pressure. This may verify if the gas valve is damaged or not. Is the supply undersized?

 

[mfgs]

The supply is slightly undersized, but not enough for it to give 6mb at max rate. Cutting in a test tee is a good idea.

 

[Nostrum]

I've got a complex with these in and a 28mm straight run up the wall of about 6 mtrs straight off the meter gives me 17mb on max, with 20.5mb @ meter so they are quite greedy on the gas without looking at the book. I'd whip the meter out and give it a shake, see if anything comes out, if it does put it back in and phone transco, it's their problem.

 

[buckley plumb]

cut in a test point under the boiler and check max working pressure. This may verify if the gas valve is damaged or not. Is the supply undersized?

i agree cut in test nipple under boiler . could also disconnect at meter and blow through with compressed air

 

[wards]

make sure before you shake the meter it has no anti tamper device fitted.

 

[AWheating]

if you cut the gas pipe see if theres a thin film of carbon built up on the inside of the pipework. this can become loose and powdery and block stuff up. It normally comes from dirty gas supplies.

 

[stevetheplumber]

i had similar inlet preasure was up one minut down the next transco replaced the supply in and it cured the problem

 

[arran197]

That's an unusual one, not sure what Transco would say tbh, they're quite lazy from what I've seen of them, they try and pass everything off!

 

[mfgs]

Just an update. I was back there today, boiler had stopped working again and would not fire up at all. Was a couple short bursts of flames on ignition but it wouldnt stay alight. Took gas valve out and it was blocked again, cleaned it out and cut a test point into the pipework just uner the boiler. Put gas valve back and still would not work. The gas pipe was very dirty inside a grey/black film all over the inside of the pipework and it was flaking off at points, so this is clearly what is causing the blockage. I replaced the gas valve and it fired up first time, not sure what the stuff is inside the gas pipe?

 

[tamz]

What you have in the pipes is copper sulphide aka black dust.
It is caused by the hydrogen sulphide in the gas (the rotten egg smell) reacting with the copper. It creates a film on the inside wall of the pipe which flakes off when the pipe is moved. Sometimes depending on the concentration of h2s in the gas, it can be quite a problem.
Only way to get cure this is repipe the gas run. When you do fit a filter before the boiler in case it builds up in the future.

 

[mfgs]

Thanks tamz. I have never seen a filter for gas before. Can you point me in the right direction?

 

[tamz]

GAS COCKS & FILTERS

4th one down although the 80 micron Y strainers work too and are easier to clean.

Happy 1000 :yes:

 

[mfgs]

Cheers, very helpful

 

[Nostrum]

I've seen this before quite a few times but never had a problem with it like you describe. Interesting to know what it is and why though, thanks Tamz.

 

[tamz]

If you cut out a bit old pipe and bang it on the ground it will surprise you the pile of dust that comes out. Some big flakes too.
Worse in some parts of the country than others but it is always there to some extent. That is what the silvery grey coating on the inside of a gas pipe is. Transco are supposed to keep the level of H2S below a certain level to minimise it.

 

[mfgs]

I've seen this before quite a few times but never had a problem with it like you describe. Interesting to know what it is and why though, thanks Tamz.

I have seen the inside of gas pipes a bit grey before, but I have never seen soo much of it come loose like this.

 

[Nostrum]

Bizarrely and quite spooky, i had this problem today. The underlying fault was low working pressure at meter but this was possibly caused by this stuff as when I removed the gas valve it was choked with the stuff? Wondering if the boiler sucking on a restricted supply line may be dislodging this stuff?

Will let you know if the problem re-occurs.

 

[tamz]

Wondering if the boiler sucking on a restricted supply line may be dislodging this stuff?

I've never really thought about that before but it could be a problem with the zpg's