Problems with Pentair MaxEtherm Heater

[tcrb]

I have a Pentair MaxETherm OM pool/spa heater (400,000 btu). About a year ago, when turned on, the blower would start, the burner would fire, but then would immediately shut down. I pulled the covers off and discovered that a pack rat had built a nest inside. Long story short, I cleaned out the nest and got rid of the rat.

After a thorough cleaning and de-ratting, the heater still wouldn't stay on, so the troubleshooting chart led me to replace the blower. The heater worked just fine for a couple of months. Then one evening I was heating up the spa and the temp got up a little over 90 degrees and wouldn't heat any higher than that. The max temp is set at 104, and the desired temp was set at 101. I went back to the troubleshooting chart and it led me to replace the High Limit Switch. I cant recall the specifics because it was probably 9 months ago, but there were other issues that came from the troubleshooting chart that prompted me to also replace the Ignition Control Module. Again, once those new parts were installed, the heater worked perfect.

But a few months later, I suddenly had the same problem. The heater would heat up to 95 and then stop and hold at 95. I replaced the High limit Switch this time and it worked like a champ...for about a month . Back to heating up to 95 and holding there.

Does anyone here have any idea what might be causing my High Limit Switch to burn out every couple of months?

Thanks in advance.

 

[ps0303]

So if you jump out the high limit the unit will light up again?

 

[tcrb]

So if you jump out the high limit the unit will light up again?

I'm not sure how to jump it out. But I've replaced the high limit twice and the unit operates just fine for several weeks and then stops heating when the temp reaches the low 90's. And if I let the spa cool down, the unit will heat it back up to 90 again.

 

[ps0303]

You just put a wire between the two connectors where the sensor would be. Just for the heck of it, how does the thermal regulator look? Granted this usually isn't a symptom of a bad regulator but worth a shot. No, these sensors should not go out like this. I would also consider the control board as the sensors plug into it but that's a bit more expensive to replace on suspicion.

 

[tcrb]

You just put a wire between the two connectors where the sensor would be. Just for the heck of it, how does the thermal regulator look? Granted this usually isn't a symptom of a bad regulator but worth a shot. No, these sensors should not go out like this. I would also consider the control board as the sensors plug into it but that's a bit more expensive to replace on suspicion.

First of all, thank you very much for your help. Today I fired up the spa. The heater kicked in as it should. But this time it took the temp right up to 101, which is what it is set for. The heater cycled off when it hit 101, but then it never came back on when the spa temp began to drop. The "Service Heater" light came on and stayed on. I turned the unit off and jumped the high limit switch as you suggested. Turned the unit back on and the burner would fire, but shut off after 4 seconds. It fired 3 more times (again, shutting off after a 4 second burn), and then the blower turned off and the "Service Heater" light came back on. So, since I get the same outcome while the HLS is jumped, I'm assuming that it's not the HLS that is my problem, correct?

At your suggestion, I pulled the thermal regulator. It did have some scale buildup around the pin, but the piston was free and moved when I applied pressure, so I'm thinking that's not the issue either. I re-installed the thermal regulator and mixed cold water from the pool to bring the spa temp down to around 78 degrees and then fired the unit up again. I got the same results as when the HLS was jumped....the burner would kick on for 4 seconds and then shut off. It did that 4 times and then the service heater light cam on again and the unit shut down.

One thing I did notice is that none of the diagnostic led's on the back of the control board are coming on, and it makes me wonder if that is any indicator that the problem is with the control board. With my past issues, those led's were instrumental in getting to the root of the problem. But, like you said, it's kind of an expensive part to buy when you're not sure. The only other thing I thought I might try replacing is the thermistor, which isn't that expensive. Is there a way to check for a bad thermistor, like jumping it?

 

[ps0303]

These kinds of issues are always fun. I would test the thermal regulator just to be sure it actually opening up. I take them out, and then close up the port and fire the heater. Hold the thermal regulator with a pair of pliers over the exhaust and watch to see if it is in fact opening. When you have the regulator out, check up inside the opening and make sure the bypass is still in place. It feels like a round button. Also, just for grins, remove one of the bottom bolts on the header and see if water comes out. Other than the fact that your system first initially ran fine, the firing for 4 seconds and shutting off with no indicator of on the board makes me point at the ignitor not sensing flame once it ignites or water in the canister.

 

[tcrb]

These kinds of issues are always fun. I would test the thermal regulator just to be sure it actually opening up. I take them out, and then close up the port and fire the heater. Hold the thermal regulator with a pair of pliers over the exhaust and watch to see if it is in fact opening. When you have the regulator out, check up inside the opening and make sure the bypass is still in place. It feels like a round button. Also, just for grins, remove one of the bottom bolts on the header and see if water comes out. Other than the fact that your system first initially ran fine, the firing for 4 seconds and shutting off with no indicator of on the board makes me point at the ignitor not sensing flame once it ignites or water in the canister.

Good call, Paul. Even though it's Easter Sunday, this thing kept bugging me, so I pulled and tested the TR per your directions and no, it's not opening. Also, I checked, and the bypass is in place and no water in the canister (at least none leaking when I pulled the bottom bolt of the manifold). I still wonder if the control board is part of the problem too, but a new TR is only 35 bucks so I'll order a new one and see what happens (fingers crossed).

Again, many thanks for the help. I'll let you know the outcome when the new regulator is installed!

Happy Easter!

 

[Pool Clown]

My money would be on the FENWAL, not main board, if not the TR. While the main board tells the heater whether to fire or not, the FENWAL is the switch that makes it happen. It switches the power to the HSI, blower, gas valve, and 20 second delay (gas valve). Since you have the TR coming, try that first. That is usually the problem.

Keep in mind that the TR controls temp of the water exiting the second pass through the exchanger. bad TR interferes with that control, and will cause higher than normal temp (hi-limit trip). Once that occurs, heater shuts down and hi-limit begins to cool and re-sets, control once again sees closed hi-limit and begins start sequence hence no lock-out.

But you are having some symptoms that aren't in line with a bad TR.

Bad TR will try to re-fire before the fan shuts down.
Bad TR usually once it has a problem, wont allow a full (uninterrupted) heat to set point, like you had.
Bad TR will eventually heat to set point, but will take a long, to very long time to achieve since the heater is cycling. You had not mentioned any cycling.
Bad TR won't cause a lock out but will cycle forever (till set point). I think you said went to a little over 90 and then no higher?

Think back to when you removed the TR, Once you removed the plug, did the TR and spring come out of the heater easily? Or did it seem to be a little hung up on something inside? A broken pressure/flow regulator would make the TR a little difficult to remove. That could be the sometimes works and sometimes not symptom you are having. Could also a gas pressure/volume issue, but were getting ahead of ourselves here. Try the TR first, and go from there.

 

[tcrb]

These kinds of issues are always fun. I would test the thermal regulator just to be sure it actually opening up. I take them out, and then close up the port and fire the heater. Hold the thermal regulator with a pair of pliers over the exhaust and watch to see if it is in fact opening. When you have the regulator out, check up inside the opening and make sure the bypass is still in place. It feels like a round button. Also, just for grins, remove one of the bottom bolts on the header and see if water comes out. Other than the fact that your system first initially ran fine, the firing for 4 seconds and shutting off with no indicator of on the board makes me point at the ignitor not sensing flame once it ignites or water in the canister.

My money would be on the FENWAL, not main board, if not the TR. While the main board tells the heater whether to fire or not, the FENWAL is the switch that makes it happen. It switches the power to the HSI, blower, gas valve, and 20 second delay (gas valve). Since you have the TR coming, try that first. That is usually the problem.

Keep in mind that the TR controls temp of the water exiting the second pass through the exchanger. bad TR interferes with that control, and will cause higher than normal temp (hi-limit trip). Once that occurs, heater shuts down and hi-limit begins to cool and re-sets, control once again sees closed hi-limit and begins start sequence hence no lock-out.

But you are having some symptoms that aren't in line with a bad TR.

Bad TR will try to re-fire before the fan shuts down.
Bad TR usually once it has a problem, wont allow a full (uninterrupted) heat to set point, like you had.
Bad TR will eventually heat to set point, but will take a long, to very long time to achieve since the heater is cycling. You had not mentioned any cycling.
Bad TR won't cause a lock out but will cycle forever (till set point). I think you said went to a little over 90 and then no higher?

Think back to when you removed the TR, Once you removed the plug, did the TR and spring come out of the heater easily? Or did it seem to be a little hung up on something inside? A broken pressure/flow regulator would make the TR a little difficult to remove. That could be the sometimes works and sometimes not symptom you are having. Could also a gas pressure/volume issue, but were getting ahead of ourselves here. Try the TR first, and go from there.

Well I finally found time to install the new TR, and that was definitely PART of the problem. Apparently the heater has not been working properly since we purchased this house and I had no idea, since this is the first pool I’ve owned. From the day we first moved in, the heater would take 2-3 hours to heat the spa up to the desired temp. The heater would cycle every 2-3 minutes during that 3 hour period, but I presumed that that was the way it should operate as I had no previous experience with pool heaters. So I was pleasantly surprised after I installed the new TR when the heater brought the spa up to 101 in only 45 minutes!

My initial thought was that my problem was solved. I let it run for an hour longer and it maintained the temp right at 101. I then switched back to pool mode to cool the water down and then back to spa mode. Worked perfect again…heated up to desired temp and cycled while holding the desired temp this time for two hours. I tested it two more times using the same sequence and it worked perfect. The next night we decided to have a soak. Kicked on the heater, and again it went right up to 101 in about 45 minutes and the blower shut down. But after we were in the pool for a half hour or so, I noticed that the water temp seemed to be cooling down and the heater had not cycled since we got in. I got out and checked, and the “Service Heater” light was on. I turned off the heater and turned it back on again. The blower came on, then the burner fired, but would go out after 4 seconds. The burner tried to fire 3 more times. It would burn for 4 seconds, and then shut off. After the 4th try the blower shut down and the service heater light came on. Checking the back of the control board, there are no lit led’s.

So, these are the exact same symptoms I had before replacing the TR except the unit now brings the water up to the set temp before it shuts down (and it now heats up in 45 minutes instead of 3 hours). The heater seems to work perfect, to bring the water up to the set temp, but now it wont hold it.

Pool Clown, you mentioned it may be the Fenwal, but I did replace that early on when I first had issues with the burner staying lit. So that unit is only about 7 months old I would think it’s still good unless I got a bad one, or something else has caused it to go bad again. Also, I clearly remember that when I first removed the old TR, I had no problem getting it out, and in fact, when I pulled the plug, it actually shot out of the manifold. So I assume that the pressure/flow regulator is not broken.

Any other ideas? Or do I bite the bullet and order a new control panel?

 

[ps0303]

Since the unit is tripping the service light but no other LED makes it an interesting issue. I have seen where the ignitor, also the flame sensor, was marginal, it would act like this. Seeing the fenwal is newer, unless you took a power hit, it should still be good unless it wasn't new to begin with. It doesn't sound like the bypass is broken because as you said "it shot out." Still could also be the control board. It's a roll the dice issue at this point unless you have meters placed in the right place to see what is dropping out to cause the unit to stop running.