Hayward H250 Heater. Starts by jumping across TH on gas valve.

[cschnurr]

We had our pool installed 16 yrs ago with a Hayward H250 heater (millivolt system). We actually only use it 2-3 times a year and each time is a struggle.
At the beginning of the year it takes about 5 minutes of holding the gas valve on 'PILOT' to keep the pilot light from extinguishing,.

Whenever I do turn the heater ON, its seems a struggle. Tonight I approached it systematically. I followed the troubleshooting guide in the manual. Pool pump ON, Pilot light lit, gas valve ON, thermostat set higher than pool water. When I jumper across the TH terminals on the gas valve, the burner lights. When I remove the jumper wire, the burner STAYS LIT. My understanding is that jumping across the TH terminals on the gas valve jumps across all components. The troubleshooting continues to determine which of the components is defective by jumping across each component until the burner stays lit.
My burner stays lit without jumpers, it just didn't start until I jumpered the all the components.

Given the rare times we use the heater, I have no problem starting the heater every time this way, but if I did want it fixed where would I start? Is this a safety concern?

Thanks,
Carl

 

[swamprat69]

Not quite understanding what you mean by "jumper across the TH terminals"? The three terminals on a Robertshaw millivolt gas valve are labeled TH - TH/TP - TP and on a Honeywell millivolt gas valve are labeled TH - TH/PP - PP. TP or PP are common from the thermopile/powerpile directly to the gas valve. TH/PP or TH/TP are the other lead from the thermopile/powerpile which then goes through all of your safeties and operating controls back to TH to supply voltage to your gas valve to operate. If you are jumping from TH to TH/PP or TH/TP and the burners then stay lit, it would seem to indicate that the problem is not with an individual safety or operating control but rather with marginal minimum voltage ( in DC millivolts ) needed to operate the gas valve. This can be due to an old/weak thermopile/powerpile or excessive resistance ( due to dirt/corrosion of contacts or poor wiring connections) in the circuit (safeties and operating controls ) from TH/TP or TH/PP to TH. This guide along with a multimeter should help you isolate the problem https://gdainfo.com/Resource1049853HJDUFOS023X/Touble Shooting/Robertshaw Millivolt Tests.pdf You can see a general millivolt wiring diagram on page 15 of this manual https://www.hayward-pool.com/assets/documents/pools/pdf/manuals/h-series-millivolt-owners-manual.pdf

 

[swamprat69]

Forgot to mention that thermopile/powerpile output can also be effected negatively (reduced) by a weak pilot flame due to a dirty pilot orifice or low gas pressure. Also (rarely) incorrect positioning of the thermopile/powerpile in the pilot flame as the voltage is created by a temperature differential between the hot junction and the cold junction.

 

[cschnurr]

Thanks swamprat69. Sorry for the slow reply, I was out of town for a couple weeks.
'Jumper across the TH terminals' is the description given in the troubleshooting flowchart on p36 of the manual you attached. I interpreted this to mean TH to TH/PP.

Its getting time to close the pool. I'll wait for a warm day to troubleshoot, or just close it and troubleshoot next spring.

 

[swamprat69]

Your welcome...best of luck with troubleshooting...will be here if you need further help

 

[cschnurr]

Thanks swamprat69.
We never used the heater this spring, but I realized that September is coming soon, so I should finish troubleshooting my heater.
My problem is described in my OP. I could get heater started by jumpering wires TH and THPP. Burner would start and remain ON when I removed the jumper.
The burner would stop when either; the pool pump was off, I turned the temp down, or I turned the heater OFF.
The only way I could get the burner to restart would be to jumper TH and THPP again.

I started at the switch, disconnected the wires and jumpered across the wires leading to the switch to remove the switch from the circuit.
If the switch were faulty, then the heater would start up without jumpering TH and THPP.
If not, I reconnected wires to the switch, and moved to the next component in the millivolt circuit and repeated.
When I disconnected and jumpered limit switch located near the floor of the heater (see photo), the burner started up.

I removed the switch, cleaned it up with some rubbing alcohol, and took a wire brush to the mating mounting surface on the heater frame.
I reinstalled the switch it and it seems to be working, even though I'm not sure what exactly corrected my problem.
Does this circuit rely on a good contact from the limit switch mount surface to the heater frame?

I can't correlate the names in the manual with their positions, because the electrical sequence of the series components was altered. (Likely by a tech I had work on the heater several years ago)
Hopefully this fix will last. In Ontario, I need to get someone with a gas fitter license to do any work on the heater.

 

[swamprat69]

From the position of the switch you are indicating it is what hayward calls a "temperature limiter switch" and most HVAC technicians know as a "rollout switch" which is positioned to detect an overheating situation outside of the combustion chamber. This switch can be can be activated to the "open" position by excessive temperature at its location due to a downdraft caused by wind (nuisance), leaves or debris blocking the vent or top of the heat exchanger or a sooted heat exchanger due to incomplete combustion from lack of regular cleaning/maintenance, The last 2 of these are more serious and need to be addressed by disassembly and inspection/cleaning as needed. Snap disc temperaure safeties are not meant to be operating controls and as such have a limited number of operating cycles before ultimately failing in the "safe {open} postion". If you have been having unobserved cycling of the rollout switch due to any of the stated reasons your rollout switch is probably tripping at a lower temperature setting than the setting that is stamped on its mounting plate. It should be replaced with a new switch and you should have your heater serviced/cleaned in order to eliminate any of the more serious causes listed as the reason for the switch tripping.

 

[cschnurr]

Thanks swamprat.
This is the first time I've diagnosed this specific limit switch as problematic. I've removed a few pine needles from the top of the heat exchanger (we don't have a vented stack) and I'll blow some air through it the fins. I definitely believe the switch was defective since since the problem was only evident on startup. After startup it closed and remained closed until power was removed. f the problem continues, I'll have someone come to service and replace the switch.

 

[1poolman1]

Thanks swamprat.
This is the first time I've diagnosed this specific limit switch as problematic. I've removed a few pine needles from the top of the heat exchanger (we don't have a vented stack) and I'll blow some air through it the fins. I definitely believe the switch was defective since since the problem was only evident on startup. After startup it closed and remained closed until power was removed. f the problem continues, I'll have someone come to service and replace the switch.

You should never bypass any of the safety items in a pool heater. That is one of several.

 

[cschnurr]

Thanks 1poolman1,
I jumpered the limit switch temporarily as prescribed in the troubleshooting guide of the manual.
Once the burner lit, I removed the jumper and the limit switch did not trigger, and the burner continued to function.
The burner never ran for any period of time without the limit switch.
For the 1 or 2 times a year I use the heater, I thought this was reasonable.
Is this over rationalizing?

 

[1poolman1]

Thanks 1poolman1,
I jumpered the limit switch temporarily as prescribed in the troubleshooting guide of the manual.
Once the burner lit, I removed the jumper and the limit switch did not trigger, and the burner continued to function.
For the 1 or 2 times a year I use the heater, I thought this was reasonable.
Is this over rationalizing?

You do this at your own risk. Using a heater with a faulty safety device is not safe. Since you know where the switch is you can see that it is easy to replace. Order one on Amazon and do it for the sake of you and your family.

 

[cschnurr]

Thanks 1poolman1. Hard to argue with your logic. If its defective, I should simply replace it.
I have a Hayward H250 heater that is 20 yrears old. I had the Pressure Switch several years ago.
Should I expect the High Limit switches to go bad sometime soon?
After I replace the switches, if I still have issues, I'll call a service technician.

Thanks