Grin. You don't trust yourself around gas, and I completely understand that point, but you trust your installer who we KNOW doesn't know what he's doing?

To be honest, I find the whole thing about number of bends in gas pipes between feed and boiler/BTU calculations seems to be very... vague. This stuff was needed for the city permit (again, something which I, uhhh, didn't do in advance because in the UK you don't ask the council when you want to change your boiler).

I never thought gas would have problems getting around corners, but it seems that it does, allegedly. Anyone know WHY?

Corners? Are you talking about gas supply or venting pipe? I'm not a pipefitter, but I've talked to a number of them while they worked on various installation I've had done. Never heard any of them mention anything about restriction on bends/corners of the supply side, only with the venting. Usually the supply restrictions were about pipe diameter and position of valves.

A corner restricts the flow, so there are charts of "equivalent added feet of straight pipe" for corners, with different values depending upon the angle/radius of the bend.

The pipe diameter also affects resistance-over-length.

So for a required flow rate (so that the instant-heater doesn't choke), there's a limit on overall length, taking into account all of the bends. Exceeding the limit, means moving up to a larger ($$) pipe diameter.

Or so the gas man said.

It's the same sort of flow calculations I had to do when sizing the dust collection tubing for the workshop.

Cheers

If it's a Baxi, try this site - the people on there know quite a bit, if you explain the problem with deftails of the status lights for each stage of the problem they should be able to suggest things to try.

The flame cycling sounds like the sensor isn't detecting that the main burner is lit, and turning off the valve and then starting over.