Heater spark and pilot valve OK, but main valve not OK

[Titanium]

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.

 

[spishex]

Yeah, trying to test those wires that both spark and sense flame is a bit of a problem.

Does it just continue to spark even though the pilot is lit? I'd consider going ahead and replacing the pilot burner assembly first, just because it's the either the flame sensor or the IID and the sensor is a lot cheaper. They also go bad more often (in my experience, anyway).

I've tried to ask both Laars and Pentair tech support about testing these sensors and their best advice was to keep one on hand, so that's what I do...

 

[Titanium]

spishex,

Thanks for the quick reply.

Does it just continue to spark even though the pilot is lit? I'd consider going ahead and replacing the pilot burner assembly first, just because it's the either the flame sensor or the IID and the sensor is a lot cheaper. They also go bad more often (in my experience, anyway).

Exactly - the electrode keeps sparking while the pilot is lit.

Thanks for the link. Which part is the flame sensor? Or is the flame sensor and the electrode in the same "spark plug" device?

After a closer reading of my heater manual, they listed another reason for my problem - inadequate flame current - which can be caused by 1) unsatisfactory pilot flame, 2) electrode configuration, and 3) poor cable and connections.

I will take a closer look at the existing pilot burner assembly and probably end up ordering a new one.

Thanks again for the help.

 

[spishex]

Yes, the spark generator and flame sensor are the same piece running on one wire. After taking a closer look at the link I posted, I notice it doesn't show the wire with it. Might want to call and make sure it comes with the wire just in case.

 

[Titanium]

spishex,

Thanks again for the reply and advice.

I did some more reading tonight and learned a ton about "flame rectification". It turns out that the owners manual for my heater actually showed an incorrect method for testing the microamp current that is produced by the pilot burner. They had showed connecting a DC microammeter being inserted between the spark electrode and the IID (ignition control) spark terminal. No wonder my multimeter got fragged.

I found a website that describes a much more logical testing method that consists of:

1) Disconnect the burner ground wire from the IID module.
2) Place the negative (black) probe of the DC microamp meter on the burner ground connection of the module and place the red (positive) probe on the burner ground wire going to the module.
3) The meter is now in series with the DC microamp proving signal coming back to the module to prove flame rectification.

http://www.willissteel.com/WSC/WSCPages/WistcoTips2.html

http://www.hvacmechanic.com/trouble_shooting/FlameFGR-2.pdf


Of course, my multimeter (even before I burned it up) wasn't going to read as low of a current as microamps, so that was my mistake on a couple of different levels.

What the above testing method is telling me, however, is how important all of the connections are between 1) the electrode/pilot burner and the burner assembly, and 2) between the burner assembly and the IID burner ground terminal. Basically it wouldn't take much of a bad connection in any of these places to interfere with a current as tiny as 1 microamp. When I said before I had checked all of my electrical connections, I had only paid attention to the IID to electrode/pilot burner connections - I hadn't realized that the ground return path back to the IID was so important.

I'm going to spend a little time tomorrow cleaning up these various mechanical connections that make up the burner ground return path back to the IID, and see if this makes any difference. If not, then I'll remove the electrode/pilot burner and do a visual inspection and cleaning and see if that makes any difference. And if that fails, then I guess a new electode/pilot burner is in my future. It looks like Teledyne Laars used a fairly common electrode/pilot burner manufactured by Honeywell for this heater - or at least the link you posted earlier looks almost identical to the electrode/pilot burner shown in the link below. https://www.acmecontrol.com/ProdImgs/Large/Q345A-1321-NEW.jpg

Also, I found several multimeters aimed at the HVAC market that are able to test current down to the microamp level specifically to verify operation of flame sensors. The cost seemed reasonable at around $200.

 

[Titanium]

Also, I found several multimeters aimed at the HVAC market that are able to test current down to the microamp level specifically to verify operation of flame sensors. The cost seemed reasonable at around $200.

I found an even better (and more economical) way to measure the microamp current involved in flame sensors and flame rectification. The cost is roughly $15 at the source in the second link below. This device plugs into most standard multimeters that accept banana plugs. [DISCLAIMER: I do not own this device, nor do I have any personal experience with Tequipment.net]

http://www.ueitest.com/IMAGES/Product Sheets/L644-DLMAT2-PS.pdf

http://www.tequipment.net/UeiDLMAT2.html