I have an old 1983 natural gas pool heater that I inherited with our house three years ago. The pool heater is a Teledyne Laars XE electronic Type ES with a 400,000 BTU capacity. This heater is mainly used to heat the attached spa, but is on occasion used to bump the pool temperature by a couple of degrees for a pool party.
The heater started malfunctioning a little last summer. I would notice that the heater would start normally, but later I would find it turned off before it had reached the setpoint. Unfortunately, the malfunction would often go away merely by opening the front service panel or even by slightly shifting some of the wiring. Very hard to diagnose and troubleshoot an intermittent problem.
This summer the problem has become even more pronounced and is finally lasting long enough to do some troubleshooting. It looks like the original Honeywell S86B ignition control (also known as the IID - Intermittent Ignition Device) has been replaced at some time in the past with a Honeywell S86F. I have verified that the control transformer, pressure switch, and both limit switches are sending voltage back to the IID when the temperature control is turned on. I then hear a click at the gas valve and hear sparking. I visually have verified that the electrode is sparking in the middle of a blue pilot flame. The high voltage wire from the IID to the pilot burner/electrode assembly appears to be in good condition and the connections on both ends of the high voltage wire look very good. I have also verified that the IID is not outputting 24 volts to the main gas valve.
So the IID is correctly sending spark and pilot gas to the pilot burner/electrode assembly, but does not seem to be recognizing that these conditions exist. Hence, no call for the main gas valve to activate.
The troubleshooting procedure for the Honeywell S86 IID suggests the following ideas for the above symptoms:
1. Check continuity of ignition cable and ground wire
2. Check that pilot flame covers electrode gap
3. Verify that flame sensing current is at least one microampere
4. If above checks are OK, replace ignition module
Items 1 and 2 appear to be OK. And I ended up destroying my multimeter trying to check item 3 (note to self - don't try and measure extremely tiny amounts of cuurent with a normal multimeter when this same tiny current also has enough voltage to produce big sparks. Duh. My only excuse is that I was tired. I really do know better.) If the IID is truly the culprit, I suppose that the problem might be in a wornout relay on the IID circuit board?
Has anyone else ran across this kind of problem before?
Thanks for any help.