How can I fix a potterton netaheat 80a?

I have a potterton netaheat 80a that is 18 yrs old. In the past few days it has begun making a loud rumbling sound when it turns on. Any ideas on whats going on?
mark henry sahim, February 2005


done
could be fan bearings. need to listen more locally. fans are easily available.

Ryan, February 2005
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