Mini max Plus 400 not firing, service light on, all other troubleshooting lights on

[bgrinstein]

The pool heater (I only use it with the SPA) stopped firing. It makes the noise usually heard when it is trying to start the pilot, does not stop doing this and never fires up. I checked troubleshooting (see attached file, Mini Max Plus Service Manual) and found that the lights all come on, including those on the back of the circuit board. That leaves me in the troubleshooting guide at "The Service Light" step which suggests checking for

1. Gas line not bled
2. Pilot orifice plugged
3. No voltage at PV terminal at gas valve
4. Defective gas valve

I have no idea how to do any of these. So I have several stupid questions: Does bleeding a gas line require a professional? How about unplugging a pilot orifice? More generally, am I barking off the wrong tree?

 

[swamprat69]

How old is the heater? Has it always worked up to this point? Are you able to use a basic multimeter to check voltages (most likely low voltage, 24 volts)? It sounds as if either your pilot isn't lighting or it is lighting but not proving that it is lit. If you can do basic electrical troubleshooting, it would be helpful if you posted photos of the controls and wiring ( especially the Fenwal ignition control ).

 

[bgrinstein]

25 years old. Was working fine up to a month ago or so. I don't use often. Then a couple of times a few weeks ago it started heating from 60F got to about 75 and stopped. Pool guy came and replaced the high limit sensor. After that it worked once, got to 100 and then it stopped, would not start again (and we got cold in the SPA). Since then I tried again starting from cold, and it wont start at all. Called pool guy again, he said it is probably the circuit board (did not come to look at it -- clearly it is not) and offered to replace the heater because it is sol old he owudl not find replacement parts (not true, I checked online).

 

[swamprat69]

If you can observe whether or not the pilot is actually lighting (possibly with a mirror down by the burners) it would be helpful. The pilot assembly is attached inside of the combustion chamber by the burners. You can tell where it is positioned by following the 1/4" aluminum pilot line that comes off of the gas valve.

 

[bgrinstein]

Thanks for the response and sorry to take time following up (went to work).
The pilot is not lighting. I removed the heater cover and looked right into it, where you described; the ra-ta-tah continuous noise comes from there, but no flame

 

[swamprat69]

Do you see a spark at the pilot assembly but no flame? There should be a spark from the electrode (the part with a metal rod through a ceramic insulator in the pilot assembly) to the grounding hood or pilot hood on the pilot assembly. The noise would indicate that a spark is being generated, but if the any part of the pilot assembly is dirty/corroded ( electrode, pilot or grounding hood or any metal to metal attachments of the pilot assembly back to case ground) it could cause the spark to be weak or spark to a location that is not in the pilot flame pattern. If there is a strong spark to the pilot/grounding hood it would seem to point to a problem with the pilot gas.

 

[bgrinstein]

I do see a spark at the pilot assembly, but no flame. To be sure I waited until dark and I see a faint glow at the assembly that turns off correlated with the RAT-TATA sounds (which I am free to turn on/off by turning the spa heat pot)

 

[swamprat69]

See attached photo of your pilot assembly. There should be a strong spark between the electrode (the metal rod that extends above the white ceramic insulator and is bent towards the pilot hood) and the pilot hood itself. If the spark is weak or occuring at another location the pilot will not light. If you only see a faint glow rather than an arc like a lightning bolt the spark may be weak due to dirt/corrosion.

 

[bgrinstein]

It's more like a glow than a spark, and a very faint glow at that. I am looking at it from below after removing the front panel of the heater, but of course is not very direct -- still I do not think my view is blocked.
So a faint spark could mean there is some dirt or rust on the electrode? If so, should i clean it, and how? Or replace it? Or have it replaced? I am getting ahead of myself, better ask: what next?
Thanks

 

[swamprat69]

Could be any of the things that I have mentioned previously. Parts of both the heater and gas train will need to be disassembled in order to inspect the pilot assembly, burners etc. . If you are not familiar with the process you should have the heater cleaned and inspected by a qualified service technician. Too many things can go wrong causing an unsafe condition if done incorrectly. At least you can tell the techinician that your pilot is not lighting and you would like the heater cleaned and serviced.

 

[bgrinstein]

Thanks!

 

[bgrinstein]

Hi swamprat69 -- if you are still there
Let me start with the questions and below I will describe how I go to this point. After opening the panel I noticed that he Gas Valve (item 17, part 073998 in the diagram for minimax plus) was switched off. Switched to on and bingo, everything works!

Here is the thing, this was the case once about 8 weeks ago. The pool guy noticed it and set it to on (and also changed the high limit). Then I used the jaccuzzi about 5 weeks ago and it stopped heating once it had reached the max temp. So the questions are: Can it just pop from on to off by itself? If so, is there a fix -- short of replacing the valve? (I am assuming the problem *is* with the valve, is it not?)

Here is how I got to this point (for amusement?): So the pool guys I contacted (recall earlier thread) did not even want to come look at the heater because it's old and one cannot get an original part replacement control panel, no matter I told them what tests it had already passed. Convinced it had to be the pilot assembly I decided to find out how to replace it (you know, youtube videos and shop online). After research but before purchasing anything I opened the heater again to see if I could disassemble the pilot and before I start I notice the gas valve at "off".

 

[swamprat69]

Gas valves will not move from "on" to "off" by themselves. Older systems that used a continuous (standing) pilot had safeties that would not allow the gas valve to open if a pilot flame was not present. Newer systems with an intermittent pilot/spark ignition use flame rectification to confirm pilot flame, but do not effect the on/off switch of the gas valve. Someone moved the gas valve to the off position from the on position.

 

[bgrinstein]

Thanks! It seems to be working fine. I was sure to move the valve all the way to ON (a little past it actually, until it clocked). Glad I did not agree to have the heater replaced (not yet!)