Calling for heat but blower is not turning on

[RenoTahoe]

New season, new mystery. T'stat is calling for heat, boiler is activating and hot water is being sent to the furnace. However the blower is not coming on. The blower does work as I turn the T'stat to on (not auto) and the blower activates. Likewise, I run the AC system and the blower activates.

Anyone up to help solve this mystery?

Thanks

 

[Fitter30]

Have a volt meter? Furnace take a pic of the wiring diagram might be on the inside of blower door. Thermostat brand and model? Have cooling on this air handler? Blower in heat could get a signal from either the the t-stat or from a fan control in furnace.

 

[Sponsor]

 

[RenoTahoe]

Here are some photos. Not too much to the controls on this one. Yes, I have a meter.

 

[Fitter30]

That honeywell control is line voltage and relays the wires are to except the small wires are 24 vac. Note that control is set about 118° turn knob down to 60° see if the fan comes on. Should be wired R to W makes on temp rise. If the temp sensing bulb goes bad control fails R to B

 

[RenoTahoe]

With hot water flowing through, meaning T'STAT is calling for heat, adjusting the knob all the way down and all the way up does nothing. I don't hear a click if that helps.

 

[RenoTahoe]

What is the purpose of the honeywell control.

 

[Fitter30]

Thinking it turns the fan on. T stat starts the boiler and pump. Sends water through air handler heats the Honeywell bulb up turns fan on. Under the cover behind the wiring is the differential setting.

 

[RenoTahoe]

Here is a pic of the label. Of course replacement units have more numbers. Thinking the T675A1540 is what I need at Supplyhouse.com. Thoughts on the replacement?

 

[Fitter30]

Fan come on when turning it down?

 

[RenoTahoe]

No, the fan does not turn on when I adjust all the way down or all the way up. I do not hear a click either like you normally with adjusting a switch like that. Do you think this switch needs to be replaced?

 

[RenoTahoe]

No change in continuity when checking with the meter either. Appears the Honeywell controller is dead.

 

[Fitter30]

Turn power off jump the the two wires together power it back up see if the fan runs. If the bulb would of lost it charge ( gas that changes pressure ) it wouldn't close the contacts.

https://www.supplyhouse.com/Johnson-Controls-A421ABC-02C-Single-Stage-Digital-Temperature-Control-120-240v-SPDT?utm_source=google_ad&utm_medium=Shopping_ntm&utm_campaign=Shopping_NTM_New_users&gclid=EAIaIQobChMIuYzF3_nZgQMVsS2tBh0s7ASlEAQYBCABEgJCDvD_BwE

 

[RenoTahoe]

Turn power off jump the the two wires together power it back up see if the fan runs. If the bulb would of lost it charge ( gas that changes pressure ) it wouldn't close the contacts.

https://www.supplyhouse.com/Johnson-Controls-A421ABC-02C-Single-Stage-Digital-Temperature-Control-120-240v-SPDT?utm_source=google_ad&utm_medium=Shopping_ntm&utm_campaign=Shopping_NTM_New_users&gclid=EAIaIQobChMIuYzF3_nZgQMVsS2tBh0s7ASlEAQYBCABEgJCDvD_BwE

Jumping the wires does activate the fan. Appreciate all the help here!

 

[Fitter30]

Was system calling for heat?

 

[RenoTahoe]

Was system calling for heat?

Yes. I turned the wall stat up to call for heat