troubleshooting pool heater

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EricVH

troubleshooting pool heater

Postby EricVH » Sun 30 Aug, 2009 20:19

I have a Hayward pool heater with millivolt control. The pilot light is lit, the thermostat is set high, and the pump is on with good water flow -- but the heater won't come on when I turn it on.

The control is Model 36D35U, Type 401, PN 1500984901F

I measured the following voltages on the gas control terminals, with the heater switch in the OFF and ON positions (voltages are referenced to the control valve body):

               OFF | ON
------------------------------
TH         0.0 V | 0.072 V
TH+PG   0.5 V | 0.38 V       <---- these TH+PG values fluctuated about +/- 0.04 V
PG         0.0 V | 0.0 V

(I think those letters are correct. "TH+PG" was obscured some by wiring, but I think that's what it said.)

Are these voltages correct, or in the valid range? I'm guessing that if these values are correct, then the problem is with the control valve; and if they're out of range, then the problem is with the thermocouple.

I don't run the heater, but I leave the pilot lit and test it once in a while. Several times when I've tested it before, I've had to try flipping the on/off switch several times before it kicked on. So I know that it's all hooked up right, and the fact that I get different values for the ON and OFF positions tells me that all of the switches and t-stat are right.

I also checked the voltage drop across the on/off switch. I didn't record the values, but it dropped to 0 (or close to it) when I turned it on, so I think the switch is fine.

Any suggestions on how to further diagnose the heater would be appreciated!


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Troubleshooting pool heater

Postby Pool Clown » Sun 13 Sep, 2009 02:31

Start jumping the safety switches. Start with the pressure switch, then both the high limits, then finally the thermostat. If after you jump those (one at a time) and the pilot is still lit, could be the gas valve.
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poolpro

troubleshooting pool heater

Postby poolpro » Sun 13 Sep, 2009 03:36

Before you begin jumping safety switches, be sure that the heater has good water flow going through it. If you jump the pressure switch while there is no flow, the heater could come on and be damaged.

You could start by jumping the entire safety loop to see if it is in the loop. Because the voltage is so low, it does not take much resistance in the wiring to prevent the heater from starting. Sometimes the problem is corrosion on the contacts.

Warning: Jumping safety switches is dangerous and you could get seriously injured if you don't understand exactly what you are doing. Never leave a jumper on a heater control.
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Troubleshooting pool heater

Postby czechmate » Sun 13 Sep, 2009 08:00

Gas appliance as a pool heater is not a bagel toaster.
Owning a Fluke or a low voltage tester does not qualify one to troubleshoot complex equipment.
I have fairly extensive education in this field and worked in it for 48 years.
The advice is simple.
If you have the complete wiring diagram and testing equipment and still have to go to theforum, it should raise a flag for you. (I would check the solenoid first and if it works, call an expert).
Your health and your equipment is worth lot more then 200 bucks!
You may even get someone there for a free estimate.
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Troubleshooting pool heater

Postby Pool Clown » Sun 13 Sep, 2009 20:51

poolpro wrote:Before you begin jumping safety switches, be sure that the heater has good water flow going through it. If you jump the pressure switch while there is no flow, the heater could come on and be damaged.

Eric stated that there was good water flow. Momentary jumping of the pressure switch to see if the heater fires will NOT damage the heater.

You could start by jumping the entire safety loop to see if it is in the loop. Because the voltage is so low, it does not take much resistance in the wiring to prevent the heater from starting. Sometimes the problem is corrosion on the contacts.

Your confusing me. First you say don't jump the pressure switch, then you say jump all of them??? Jumping the entire safety circuit does not tell you which safety switch is not working.

Warning: Jumping safety switches is dangerous and you could get seriously injured if you don't understand exactly what you are doing. Never leave a jumper on a heater control.

I probably should have said this in my first post:
The thing you should do when trying to fire the heater, is to stay clear of the burner tray (don't be all bent over right over the opening to the heater). That, and the fact that this is a gas burning appliance and if you realize this going into it, you should be exercising the proper amount of caution.



I too have worked on many a millivolt heater, for the most part, is not real complicated. Electronic ignition is a different story, and I agree, it is not for most DIY'ers.

"If you have the complete wiring diagram and testing equipment and still have to go to theforum, it should raise a flag for you."

I disagree. The fact that he came here for advice/guidance rather than tear into it without any advice speaks volumes to Eric's ability to be able to trouble shoot his heater safely.
Factory warranty service for Pentair, Jandy, Raypak, Polaris, and Paramount pool cleaning systems.
PoolPro

troubleshooting pool heater

Postby PoolPro » Mon 14 Sep, 2009 14:20

"Before you begin jumping safety switches, be sure that the heater has good water flow going through it. If you jump the pressure switch while there is no flow, the heater could come on and be damaged." - PoolPro

"Eric stated that there was good water flow. Momentary jumping of the pressure switch to see if the heater fires will NOT damage the heater." - Clown

It is still good advice to remind someone to make sure that there is sufficient water flow before jumping the pressure switch. If the heater fires without good water flow, it WILL damage the heater. Furthermore, your advice did not say anything about "momentarily" jumping the pressure switch; it just said to jump it.

"Your confusing me. First you say don't jump the pressure switch, then you say jump all of them??? Jumping the entire safety circuit does not tell you which safety switch is not working." - Clown

I never said not to jump the pressure switch. Jumping the entire loop will tell you if the problem is in the loop or if it's something else such as the valve or pilot generator. If it's not in the loop, then there is no need to waste time checking individual control loop components.
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Troubleshooting pool heater

Postby Pool Clown » Sat 19 Sep, 2009 23:56

"It is still good advice to remind someone to make sure that there is sufficient water flow before jumping the pressure switch."
Pool Pro

I agree, If it had not been covered already, by the poster, Eric.

"If the heater fires without good water flow, it WILL damage the heater."
Pool Pro

Not really, the high limit(s) will shut the heater off before any damage would occur.

"Furthermore, your advice did not say anything about "momentarily" jumping the pressure switch; it just said to jump it."
Pool Pro

I would consider it an insult to Eric's' intelligence to think that he would jump the pressure switch and walk away from it.

You yourself suggested jumping all the safety switches, and said nothing about it being momentary either. If he did jump the pressure switch and walked away, The heater would run till it hit the high limit (somewhere around 108). If he jumped all the safety switches and walked away the heater would run away till it had an event. Which way is more dangerous do you think?
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PoolPro

Troubleshooting pool heater

Postby PoolPro » Sun 20 Sep, 2009 01:39

Pool Clown wrote:Not really, the high limit(s) will shut the heater off before any damage would occur."


If the heater fires without good water flow, it WILL damage the heater.

Pool Clown wrote:You yourself suggested jumping all the safety switches, and said nothing about it being momentary either.


Reread my post where I say not to leave the jumper on..
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Troubleshooting pool heater

Postby Pool Clown » Sun 20 Sep, 2009 09:59

PoolPro wrote:
Pool Clown wrote:Not really, the high limit(s) will shut the heater off before any damage would occur."


If the heater fires without good water flow, it WILL damage the heater.
Ok, what exactly will be damaged? And don't say "the heater".
Pool Clown wrote:You yourself suggested jumping all the safety switches, and said nothing about it being momentary either.


Reread my post where I say not to leave the jumper on..
Factory warranty service for Pentair, Jandy, Raypak, Polaris, and Paramount pool cleaning systems.
PoolPro

Troubleshooting pool heater

Postby PoolPro » Sun 20 Sep, 2009 12:43

Pool Clown wrote: Ok, what exactly will be damaged? And don't say "the heater".


Have you ever heard a heater fire up with no water flow? It makes a loud banging noise. That noise is the metal heat exchanger rapidly expanding due to overheating. The metal can be permanently damaged.

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