I think that this might be a function of the injector and mixing arrangement with the fan.
Mine has a fairly similar arrangement with the injector and fan, although the gas feed is at the back. I asked the manufacturer about it because there was no mention in the commissioning instructions regarding pressure test, even though there are nipples on the gas valve on the input and output side.
They told me that the setup procedure doesn't involve the equivalent of burner pressure testing and in fact, if measured it would show anything from slightly positive to slightly negative. Instead of this, there are adjusters on the gas valve - one for the burner running at minimum level and the other for maximum. A combustion analyser is used and the CO2 level measured at either end - it's a bit iterative and took a little while to do. It has to be within a range at either end. They then call for a CO check at top and bottom as well which must be less than so much, The input gas rate is also checked at top and bottom as well.
IIRC, the Keston has a similar procedure.
So how did you manage?
.andy
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