Thanks everyone for your replies to my query.

I've emailed Trane but have as of yet not received a reply so, I have
gone ahead anyway and installed a Trip-Lite surge suppressor (3500
Joules) and now have a plug-in furnace. Due mainly to the exhorbitant
cost of a new processor board (not much technology or componentry for
the price indeed), I felt a surge suppressor was required in any case,
no matter what else may be wrong with the thing.

The Trip-Lite also has coax and phone line suppression just in case I
want to connect my furnace to the internet

In regards to the suggestion for a UPS, I do have a spare 300 Watt
unit but decided against trying it as it does not have sine wave
output and I question whether 300 Watts is enough to power the blower
motor plus all the other stuff.

I considered wiring the Trip-Lite directly into the breaker box to
eliminate a junction point but am probably challenging the electrical
code enough as is, what with a plug-in furnace, so decided not to.

Now, to wait and see what happens.............

Laurie Forbes