Honeywell/Aprilaire humidity sensor failure

I have an Aprilaire 600 whole house humidifier controlled by Honeywell PC8900 thermostat. For a while now the PC8900 has been showing "Humid--%", which according to the Owners Manual means that I have a humidity sensor failure.
Is this a sensor inside of the PC8900? If so, is it something that can be replaced or do I just need to order a new thermostat?
Could any indirect reason (i.e. solenoid valve failure) cause this error message.
Appreciate any input
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On Sun, 04 Mar 2007 15:12:42 -0600, pietu <pietu1_at_juno_dot_com> wrote:

We all know its your thermostat. Get a new one. You might want to get an extra one as a spare. They fail quite frequently. Bubba
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Bubba wrote:

Thought so. Unfortunately it seems Honeywell no longer makes PC8900 or any other model with a humidifier control built in. It looks like White Rodgers model 1F97-391 would have it, for a hefty price though. Is it safe to assume that all these are compatible as long as I can get the wiring right?
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On Mon, 05 Mar 2007 00:02:49 -0600, pietu <pietu1_at_juno_dot_com> wrote:

Just replace the low voltage wiring from the humidifier to the new stat and you should be good to go. The stat needs to match the new wiring for correct operation. Bubba
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"pietu" <pietu1_at_juno_dot_com> wrote in message

Use a Honeywell Model Number:TH9421
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Your sensor is easy to replace.
http://www.iaqsource.com/index.php?module=search&searchtext 089H1007&search=Go
Buy one there for $29...
Find the 2 wire that runs from the furnace to outside. It Should like the same wiring that goes outside to the air conditioner.
-Canadian Heat
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