Electric furnace doesn't turn on when call for heat

[andre.dsouza]

Hi All.

I have an electric furnace (Stelpro SEF2021) and Honeywell Pro with 2 wires (R & W).  I've had an intermittent problem where the furnace does not turn on when heat is called for.

Jumping R and W always turns the furnace on, which is why I bought a brand new thermostat, but i'm having the same issue.  In addition, the furnace works immediately when I probe R and W at the furnace with a multimeter.  It has always shown 0 - 0.5V when heat was called for, which is normal. 

Ive created a youtube video of this phenomonon: https://youtube.com/shorts/RP56xllw-IE

 

 

[scarey8]

The furnace is driven by the thermostat yes, but on an electric furnace as you have, the electric elements and blower are controlled by sequencers.  These are kinda like timers, when the signal to them is made to them they actually heat up and change position of the contacts.  They have a heat up and cool time, often have gold lettering on them which was H1-90 which indicates they start working up to 90 seconds after power being applied, C1-90 indicates they take up to 90 seconds to returned to their at rest position with respect to contacts.    nearing the end of your video before the fan turns on, there is a metallic click noise, which is likely the limit on one of the elements opening as the electric element had heat and actually over heated without the fan.  few seconds later the fan operates.  IF you have an amp clamp you can prove this by seeing amperage draw before you hear the fan activate.  The fan does not immediately activate on your furnace when R and W are connected, and I think you are expecting to hear the fan run sooner.  Track down the failed or failing sequencer and this will be your fix, or as an easier fix, add a wire from W to the G terminal, fan will activate immediately on every call for heat. 

[andre.dsouza]

Hi Scarey.  Thank you for the reply.  I will look into sequencers.  The temperature had dropped over 5 degrees celceus and was likely not going to come on if I hadn't tested the voltage across R and W