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Working gas pressure on Vaillant ecotec 630

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British Gas servicing the above boiler ramped up the boiler to maximum in the installer menu to do flue gas analysis.

They also measured the working gas pressure on the gas valve test nipple. This fell to 8mbar on maximum and 17mbar on high setting.

They then removed the isolation valve under the boiler and an amount of black sulphide dust was emitted, maybe quarter a teaspoon. They have now said the gas pipeline is blocked with the black dust restricting gas flow.

The pipe run from the meter is long at about 15 meters. The first 14m is 28mm copper and then up through the floor at 22mm and into 15mm just before the isolation valve.

Pipework is 10 years old.

After removing the isolation valve and blasting gas through the pipe no more black dust was ejected.

Does it sound feasible the pipework can be blocked by this?

The run is under a suspended floor the whole length of the house. It will be a real mess to renew.

Any thoughts? Is his diagnosis correct. Are there services which will camera or pressure clean the line?
You can get quite a build up but I have only seen it clinging to pipe walls and curling off like shale. It is fine and delicate stuff, almost like graphite. It would normally come out with a good purge. As @gmartine above said, gauze filter/strainer in gas valve is the likely cause of the pressure drop. You can fit an additional external one before the appliance that will hold more of it than the one in the gas valve does. These should be cleared out at annual service time.
had this years ago it collected at the bottom of the pipe just off the gas meter. as it went down under the floor.
Thank you for the replies.

I had another engineer out and this is the best answer I can give.

Working gas pressure at the Gas valve was again single figures. He removed the gas valve - there is no obvious filter - and tapped out a reasonable amount of black dust and cleaned it all up.

Re-installed the valve and the pressure at max load was > 15mbar and flue gases all ok.

I can only conclude that the test nipple must be post the main gas valve and before the step valve and that this was not opening properly due to the black dust.

I will look for someone to install an in-line filter near to the boiler to prevent a re-occurrence

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