Furnace only lights occasionally when we turn up the thermostat. It will work ( on and off) for some time and then not light.

Does it not light at all, or does it light and go back out after a few seconds?

Does it not light at all, or does it light and go back out after a few seconds?

Doesn't light. When it does light it works for a while (re-lighting) but then doesn't light

Does it attempt to light (glow plug glows, or sparker is sparking)? Do you hear the gas valve click and gas flow when it should be lighting?

Does it not light at all, or does it light and go back out after a few seconds?

Doesn't light. When it does light it works for a while (re-lighting) but then doesn't light

Does it attempt to light (glow plug glows, or sparker is sparking)? Do you hear the gas valve click and gas flow when it should be lighting?

Don't know about the glow plug. It's not visible with the cover. I can't hear the gas valve open even when it works

You will have to take the cover off and watch exactly what is happening and in what order for me to be of any help. Sometimes these things can be tricky to trouble shoot hands on, let alone over the web. Hope I can help.

You will have to take the cover off and watch exactly what is happening and in what order for me to be of any help. Sometimes these things can be tricky to trouble shoot hands on, let alone over the web. Hope I can help.
Thanks

Welcome