I have a Peerless Firefire 210 and after it responds to call for heat I see the input dropping to 1% and the motor sounds like it is stalling and the entire unit shakes. This happens reliably every 10-30 minutes.

Any ideas?

If it is a Pure Fire here is the second version of the manual.

http://www.google.com/url?sa=t&rct=j...8FgxJ-t43UqKBQ

I must ad that these are not your average homeowner serviceable units and you should call for ON SITE help since trying to repair one of these here by posting is all but impossible. From the sound of what you are saying it probably needs to be cleaned/serviced/with a fine tune adjustment.

I will call my the appropriate repair folks but the one I had on Saturday had NO IDEA and wanted to do something radical with the air and vent pipes. I really need someone with experience with this unit

One more thing I noticed is that this shaking occurs only when the "Input" drops to 1%. It then shakes and then goes through the cycle.