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Old Account
As you say you've got quite few up and downs of pipework which means air will be collected there too. Have you got any dead legs ? As harvest mentioned you definitely need the right amount of Inhibitor ( 2 bottles x100 sentinel ) which covers your system.Its a big house..15 rads with 2 very big doubles rest are singles. Lots of drops too if that helps as downstairs floor is concrete.
I put 1.5 bottles of sentinal in.
Also Ive tried igniting the gas but it didn't ignite so dont think its hydrogen.
Is just a thought could there be an AAV faulty and draw air in ?