Hi Steve
Had the same fault as you - was looking for a clue when I saw your question... we cleaned everywhere we could reach and exercised the connectors everywhere, pushed anything that looked like it could be pushed.. etc including what we took to be the NTC - and hey presto the fault disappeared - ie it was a gremlin, not a proper failure.
Doubt this helps you?? but it 's hopefully bought us time to save for a replacement.
Ann and John
September 2005