electricalfurnace
Rural USA. We just had a gas furnace installed. The new furnace has a 1-gang junction box with a switch and a fuse.
It's the 21st century, here, I swear. And not England.
The furnace circuit is tip-top. It's punched down into a modern service panel with perfectly typical 15A breaker, and if it needed something special, that really wouldn't be a problem.
So why does the furnace also need a fuse?
I had the exact same symptoms with my natural gas furnace, and it turned out to be the flame sensor.
It's an L-shaped metal bar (but can also be straight, depending on model) that detects if there are flames actually coming out, and turns off the gas if not. It had a white high-temp wire connecting it to the control board. Taking it out, cleaning it with some steel wool fixed the problem for me.
If yours is like the above, you'll only see the back part of it and the bracket, as the L-shaped end is inside the heating unit.
Brand probably has nothing to do with it. You'll need a service call, and should already have made one (yes, you had it serviced - but it's not behaving correctly, so you need another one.)
Clogged nozzles are a common issue, but not the only one - bad or dirty flame sensors, bad high voltage ignitors, bad control systems are all possible issues. You may need a new filter as well - if there was a lot of crud in the tank the new filter could be clogged.
If you have a power vent rather than a traditional chimney, the possible causes of abnormal shutdown increase.
Best Answer
You have an electrical connection to the Furnace - even if it is gas. Blower motors and control circuits require electricity; should you have a short - you will need the overload protection to prevent a fire that only a pyromaniac could enjoy.
The fuse is most likely of a lower amperage than your Circuit Breaker - it guarantees the safety of the furnace - regardless of your Circuit Breaker.
Think on this Why do Microwave Ovens have Fuses in them or other appliances such as TV's have fuses in them when we have these wonderful circuit breakers installed?
In Summary: The consuming unit may not trip the breaker, and if not a fire could easily erupt first before that breaker ever went into overload.