No pilot sensed AFTER heating for 10-15 minutes

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christo

christo

0
Aug 8, 2014
49
bannockburn/md
raypak natural gas heater with electronic ignition. Heats for a while - to about 86 - before it gives no pilot error. Just replaced pilot with new and got the same thing. Unit is <3 years old. Prior raypak worked consistently for 13 years. What next?
 
Check the fault history while the heater is running.

Service Menu and Fault History
To access the Service Menu and fault history, press the MODE and UP buttons simultaneously for 3 to 5 seconds. The heater will continue to operate normally while in the Service Menu. The first screen displayed is the Flame Strength indicator, which indicates the pilot flame current using a bar graph and numerical display. A signal of less than 4 indicates a weak flame signal and may require service. Refer to Section 5 Troubleshooting for possible causes and corrections.

Press the DOWN button. The Supply Voltage screen indicates the voltage supplied to the control board.
Normal readings range from 24 to 29 volts.

Press the DOWN button. The Run Time indicates the total hours of operation for the pool heater, as measured by the amount of time that the main gas valve has been powered. The Cycle count indicates the number of on/off cycles of the heater, as measured by the number of times the pilot valve has been powered.

Press the DOWN button. The Fault History can display up to ten faults in memory. The order of the faults begins with “Fault Last,” which is the most recent fault, and proceeds through ten most recent messages in chronological order. The second line of the display shows the fault message. If there are no faults in the history buffer, the second line reads “All Faults Clear.”
Click to expand...
 
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JamesW said:
Check the fault history while the heater is running.
Click to expand...

8.0. Fault history shows several hi limit 2 errors.
Just ran it.
Heating til about 87.
Showed hi limit 2 fault.
Temp kept going to 89.
Temp dropped to 87 and hi limit disappeared. Replaced with spark followed by no pilot sensed.
Fault history showed hi limit at number 2, 5 & 7. All others are no pilot.
Hmm.
I guess normal cycling is not supposed to cause hi limit 2?
 
High limit might be a bad Unitherm Governor.

What is the flame strength?

It looks like the water could be overheating causing the high limit error, which shuts off the heater.

Then, when the water cools and the high limit clears, the heater tries to restart and is not getting a good flame rectification microamp signal.

A weak signal could be due to low gas pressure, a bad gas valve, a flame sensor failure, a bad ground, a bad control board or several other problems.

Have you verified the gas pressure?
 
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I would check the unitherm governor.

This is a different heater, but basically the same thing.


The pilot not relighting can be multiple things. The flame strength looks good, so maybe it's an intermittent issue.

Maybe check the gas pressure to make sure that it's good while the heater is running.
 

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swamprat69 said:
What speed are you running the pump at?
Click to expand...
2750 rpm. Max is 3450 rpm. Testing showed that was enough to get the heater to run without low flow error.
JamesW said:
I would check the unitherm governor.

This is a different heater, but basically the same thing.


The pilot not relighting can be multiple things. The flame strength looks good, so maybe it's an intermittent issue.

Maybe check the gas pressure to make sure that it's good while the heater is running.
Click to expand...
is that the part that cycles the heat to avoid heating too quickly? Seems like it couldn’t get hi limit if it were cycling normally.
Fairly confident of pressure - upgraded the main to 2# when installing the pool heater which has its own .5# line. So I should have enough to heat pool and house.
 
The unitherm governor blocks water from exiting the heat exchanger until it gets warm.

It prevents condensation from forming on the heat exchanger from cold water going through the heat exchanger.

If it's not working correctly, the water will overheat and trip the high limit.

I don't know what part you're talking about that cycles the heater on and off.

In any case, I think that you have two issues.

I would check the unitherm governor and replace it if necessary.

As to the flame sensor failure, that can be many different things as noted previously.
 
I thought the normal heating operation cut the heat when the output temp exceeds the input temp by a certain threshold. Rather than firing constantly until target temp is reached. Is there a thermostat part that does that threshold checking and cycling?
 
JamesW said:
There's nothing that measures the heat rise.

I would check the unitherm governor and the gas pressure during operation.
Click to expand...
so how does the heater cycle while heating?
Run Time 73h
Cycles 1321
is a cycle count one demand for heat? or the on/off while heating to the target?
if the unitherm governor weren't opening would any hot water be going to the hot tub?
mine does output hot water back to the hot tub. before it gets the hi limit and shuts off than fails to restart with the no pilot sensed. so how could it be a fault unitherm governor?
i don't have a gas pressure meter. maybe time to call a raypack certified tech?
 
A cycle is any time that the heater starts and stops.

Once the heater starts, it should run until it reaches the set point.

If the unitherm governor is not opening all the way, the water in the heat exchanger will get too hot and trip the high limit.

This is called short cycling because it's stopping before it reaches the set point.

If the unitherm governor is opening part way, the water will be warmer at the exit than the inlet.
 
Really? So all this time when the hot tub was heating and it would shut off for a few minutes before it would fire up again - it was throwing hi limit errors than restarting? I guess that would cause way more ignitions/cycles that running continuously until target it set. So getting from 80 to 100 should count as 1 cycle? I have 1324 cycles.
So it should be fully open to allow all the heated water to exit rather than partial open which causes over heating? At what temp is it supposed to open? Fully closed means water doesn’t enter the heater?
Thanks for all you info so far.
 
Condensation Protection
The Unitherm Governor inside the header helps reduce condensation from low inlet water temperatures. It automatically regulates the water flow to help keep the water temperature in the heat exchanger above 105°F. Both water temperature and water flow rate are controlled to eliminate condensation, sooting, and scale build-up that can shorten heater life.

High Flow Rates
The Raypak gas heater comes with an automatic bypass built into the header. You'll find that the heater is capable of handling water flow at a rate up to 125 GPM.
Click to expand...

The patented Unitherm Governor is a thermostatic mixing valve specifically designed to maintain constant heater internal temperature between 105° to 115°F despite continually changing flow rates from the filter and changing pool temperatures. This narrow range is needed to prevent damaging condensation on the burners which will occur if the heater runs for any length of time below 100°F.
It is also needed to inhibit scale formation in the tubes by maintaining temperatures well below accelerated scaling temperatures.
Click to expand...

If the heater is shutting off before reaching the set point, there's a problem.
 
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ordered the unitherm governor. should arrive tomorrow.
given 73 hours of run time and 1324 cycles - it seems like i have been getting hi limit errors ending cycles for some time - perhaps since the heater was installed about 1000 days ago.
i heat the whole pool in the spring to take the chill off early to about 80. i heat the hot tub maybe 15-20 times a year for actual use.
during the winter i close the pool but run the hot tub (and all the equipment) with the heater set at the lowest possible setting (55?) to ensure nothing freezes. and the variable pump set to a speed that maintains adequate flow to heat. no freezing issues.
assuming i never run the heater for less than 30 minutes at a time those 73 hours equate to 146 1/2 hour "cycles". yet i have almost 10 times that number.
yet until i changed the ignitor the only faults were no pilot.
is it possible my unitherm governor was bad from the start? and after 500 hi limit errors the igniter went bad?
i guess over the winter the heater would fire to stay above 55 and shut off after a hi limit error - which was enough to avoid freezing.
 
It seems like an excessive number of cycles.

Excessive cycling can be from a bad unitherm governor, bad internal bypass or low flow from the pump being set to too low rpm or a dirty filter.

Maybe excessive cycling created excessive wear on the pilot gas valve?

Maybe the gas valve pilot valve sticks sometimes?

The flame strength looks good. So, I would think that the gas pressure is probably good and that the flame current sensing system is probably ok.

So, I think that you need to address the short cycling and the intermittent pilot lighting failure.

Replace the unitherm governor, make sure that the filter is clean and make sure that the pump rpm is sufficient.

If the short cycling continues, I would check the internal bypass.

For the pilot lighting failure issue, maybe contact Raypak and see what they recommend.

You might need a new gas valve, but an intermittent issue can be difficult to definitively diagnose.
 

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