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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I have a unit heater with a Honeywell S8600M controller. It

Customer Question

I have a unit heater with a Honeywell S8600M controller. It works good as long as there is a certain period of time between cycles. But if it is cold and it has a shorter period of time between cycles it will go through the 90 second trial for ignition, with the fan running for approximately 5 minutes then start the 90 second trial for ignition again. It will ignite and heat again as normal. Is there a time delay that must be met between cycles and if so is there a way to change or eliminate it? if not is there a problem with the controller, gas valve or pilot?
Submitted: 1 year ago.
Category: HVAC
Expert:  Tim H. replied 1 year ago.

Hi, I'm Tim and I'm an HVAC expert here to assist you with your questions. Please provide all information I request as it makes it more difficult to troubleshoot something when I'm not there onsite. Essentially, you become my eyes and ears. Thanks for the opportunity to help. At the end of our dialog, you will have a chance to rate my service, but please wait until we are finished and you're satisfied you have all the information you need.

What is this on? Make and model please? What exactly happens to the burners when it malfunctions?

Customer: replied 1 year ago.
It is a Modine natural gas unit heater model PD 100AE0130. When it malfunctions I can hear the igniter firing but the pilot doesn't light. Since the polite doesn't light the burners don't ignite either. The fan continues to run for about five minutes then it starts the pilot ignition process again. The pilot lights, ignites the burners and it works until it reaches the set temperature and shuts off.
Expert:  Tim H. replied 1 year ago.

Does this unit have a flame sensor and hot surface ignitor or a spark ignition? In other words, what is the full model of the Modine heater?

Customer: replied 1 year ago.
That is the full model #. It is spark ignition.
Expert:  Tim H. replied 1 year ago.

Does your pilot ignitor look like this?

Customer: replied 1 year ago.
I haven't taken it apart to find the ignitor. I wont be able to do that until tomorrow.
Expert:  Tim H. replied 1 year ago.

OK, let me know. What is happening here is your pilot is not sensing the pilot flame which is why the unit (and control) keeps restarting until it locks out.