I need help troubleshooting

ArchieM42

Good afternoon. I was an HVAC tech 3 decades ago, but never worked on recirculating systems. Only traditional heating systems ( ducted ) and now need to troubleshoot my own recirculating hot water system. 

I get spark, and circulation of the water ,but nothing else. I’ve checked a limit and roll out sw. both are closed. 

I’m posting the diagram that is on the side of the unit. Any assistance would be appreciated. 

EdTheHeaterMan

Do you know the sequence of operation?
1. Call for heat from thermostat
2. 1K relay coil is energized
3. 1K1 relay contact is closed, the circulator pump is operational
4. 1K2 relay contact is closed sending power to the vent damper (if the limit switch is closed)
5. Vent damper opens and the end switch contacts make to power the ignition control
OR if no damper:
6. Ignition control is powered. (If the spill switch and roll out switch are closed)
7. Spark is energized and the gas valve opens
This may be where your problem is since you have spark and circulator pump operation
8. The gas is ignited by the spark at the pilot burner
9. The flame sensor reads the flame signal and opens the main valve so the gas ignites at the main burners.
10a. If the call for heat continues and the water temperature reaches the limit switch setting temperature then the burner stops but the circulator continues
10b. if the water temperature drops the burner will relight starting from step 6.
10c. If any other limit opens the burner will stop but the circulator will keep operating.
10d. The call for heat is satisfied and the burner and circulator stops.

ArchieM42

Thanks for replying, no I do not know anything about this unit.  

Teemok

If you're getting no pilot flame but spark. Do you have incoming gas is first check. If yes, confirm 24v between PV/MV (com) and PV at the gas valve terminals while sparking is happening, I would suspect a clogged pilot but would confirm the pilot valve is opening with a gas pressure test at the pilot tube port before I pull it out. If gas pressure is present, it's time to pull and clean or replace the pilot.

EdTheHeaterMan

I have posted the Sequence of operation above ... see the edit above.


you will need to check for 24 volts at the gas valve on the PV/MV terminal to the PV terminal to see if the ignition control is operating properly. If not then you have a defective ignition control.
if yes then you need to check the gas valve for proper pressure. I have been called to check an electrical / control issue more than once, only to find the gas has been turned off.

EdTheHeaterMan

EdTheHeaterMan

By the way... the gas valve works the same way on boilers as they do on furnaces. so checking for voltage at the gas valve and looking for blockage in the pilot burner or proper gas pressure is the same.

gas + spark + oxygen = flame. if you get all three in the right place you should have heat

ArchieM42

This is amazing. Thanks everyone for the fantastic support. I’m going to check those things asap.