Gas Pipe blockage causing no pressure at boiler?

[plumbgaspaul]

I am looking to double check and ensure I am not missing anything obvious before updating landlord on what I think is a gas pipe blockage.
I attended a property that had a Worcester Greenstar 24i Junior. Tenant stated no hot water in bathroom taps, ok in sink for short period and flame reduced on gas hob when hot water running.
At gas inlet on boiler pressure reduced from 21mbar down to 0mbar once boiler fires up. Checked same at meter test point and was 22mbar with no drop. I spoke to Worcester and they stated that problem was probably regulator at meter. Found this strange as test point after regulator but called out SGN who replaced regulator. Issue remained the same. Gas pipes have been in place for over 10 year (possibly longer) fault only recently began. Gas pipes are under floor so difficult to access.
Is the issue a blockage in the pipe?
If so is there anyway to try and clear blockage?
Or is only solution to provide a new gas pipe run to hob and boiler?

Thanks for any advice -

 

[ShaunCorbs]

I would cut in a test point Below the boiler

Gas valve could be dirty / stuff in it

 

[plumbgaspaul]

I would cut in a test point Below the boiler

Gas valve could be dirty / stuff in it

Why would the gas hob flame be effected if the issue was the gas valve?

 

[ShaunCorbs]

Why would the gas hob flame be effected if the issue was the gas valve?

Didn’t say there was an issue with the hob

 

[ShaunCorbs]

If the hobs affected then gas line

Remove the meter hook an air compressor to the boiler connection and blow back to outside

Also do this on the hob feed eg from inside out but cap the boiler feed

 

[plumbgaspaul]

Didn’t say there was an issue with the hob

The flame reduced on the hob when hot water running. (Mentioned in original post but perhaps not very clear, apologies)

 

[plumbgaspaul]

If the hobs affected then gas line

Remove the meter hook an air compressor to the boiler connection and blow back to outside

Also do this on the hob feed eg from inside out but cap the boiler feed

Thanks Shaun.

 

[Last Plumber]

I would check inside the Gas Valve filter first of all. It could well be the dust/shale resulting from Sulphidation. See this link.
The reduction on the hob could be related but it could also be a pipe size issue which has always been there. To have zero pressure at the inlet to the Boiler is likely a blockage in my opinion.
I have not seen it so I could be wrong!