Helio-Matic 4000A Baulky Rheostat?

[bmorril2]

Have older 90's model Helio-Matic 4000A controller , tracked my problem to valve not opening and closing properly to bad Rheostat( knob adjuster for temp.),can I get the rheostat separately or whole controller and will the newer 4000C work .
Thanks

 

[JasonLion]

If you are handy with electronics, it is possible to fix the Rheostat, but I don't recommend trying unless you already have experience with soldering.