# Posted: 23 Mar 2021 18:32
Gas supply lines should never need cleaning.
If a two-stage burner is not kicking into high it is usually because the ambient temperature is high enough for the thermostat setting that high is not needed. With my thermostats connected to variable output heaters, I can trick the system into kicking into high output by setting the thermostat to a very high temperature, like 90 F or more. My thermostats go up to a high setting of 99 F (digital). If the burner switches to high when that is done then there would seem to not be a sufficient differential between the ambient temperature and the setting on the thermostat.
Or there is a problem with the thermostat, or the valve solenoids. Or something.