Nick,

Pouring acid in the heat exchanger is not a good idea, ever. The acid will eat it up!

Post the rest of the pool's chemistry numbers.

I suspect that you have a very high calcium hardness level combined with a high pH. This causes scale to form. With high calcium hardness in the pool, I like to see the pH down around 7.3, give or take a tenth. This will also help your reduce your frequency of cleaning for the salt cell. This will help keep the calcium in solution.

Are there any yellowish/off-white deposits forming on the pool walls?

Test your fill water too. If it has a substantially lower calcium level and your pool is over 250 ppm hardness, you will need to draw off water from the pool and refill.

Salt cells tend to push a pool's pH higher. Adding MA is a normal and expected process to help keep it in check.

The only way to check this heater's exchanger is by a nearly complete tear down by a trained technician. This is not a DIY job. Given what you said about only recently gotten your pH down to 7.8 suggests you had an extended period where the pH was substantially higher, a condition that makes calcium form scale deposits fairly quickly.

If you did clog the heat exchanger with scale, it will need replacing and it won't be under warranty. No brand of gas fired heater that I know of would be since scaling is a poor chemistry problem.

I suspect though that the issue isn't scale in the heat exchanger yet. I suspect the the flow switch is possibly scaled and having having difficulty making it's contacts. Another potential is a clogged filter causing low flow.

A great resource for understanding pool chemistry is found at Trouble Free Pools web site. While I don't subscribe to the use of the BBB system, particularly if pets and small children are present, that they suggest, the rest is very,very valid and useful. I highly recommend it.

Scott

High limit switch. You probable need to clean or replace the sensors. You could jumper it at the thermal sensor temporally to troubleshoot. Most heaters have led indicators on the back of the circuit board that will tell you which interlock is tripping.

If the heater is short cycling most likely your thermal regulator has failed due to bad water chemistry/corrosion or electrolysis issues. Replace thermal regulator and look at the old one to see if it has turned green or corroded. If this is the case you have to make sure your heater is electrically bonded and check your water chemistry on regular basis.

This has something to do with your pool water, have you check your water chemistry?

Here is a link that might be useful: Spa Heaters

I have the Sta-Rite Max-E-Therm pool heater as well, and it was cycling on and off every 45 seconds exactly as described in the first post of this thread (nick_shirley). I replaced the high limit switch based on another blog I found, and that didn't do it. Turned out to be the thermal regulator (part 77707-0010), which was stuck closed by scale as described by dapooltec above. Takes 5 minutes to pull it and replace it with the new part. Part sells for $55-57, not including shipping/tax, at several sites on internet. Scaling is definitely a water chemistry problem, but I suspect you're going to get some scaling on this part after 4-5 years even if your alkalinity/pH has been kept in good range. I have a concrete/rock pool and probably should have been adding acid more frequently after the pool was first installed, when the concrete is leaching heavily and pH tends to be very high/alkaline.

You folks are great! I finally decided to pull the thermal regulator (really just a small automobile-type thermostat) and tested it. Didn't move at all even when I dunked it in boiling water. I was hoping that just removing the gunk that had built up on it would help but after a while I realized that there was a tiny hole in the cylinder. Ordered one on-line for about $42 including shipping, swapped it in, and now my heater works perfectly. The replacement, as boatbuilder306 indicated, was a snap. Just unscrewed the access plug, pulled out the long spring, replaced the thermostat, and screwed it back in.

In reviewing my original post, I see that I claimed the "service system" light was on. Maybe it was at the time but since then it was the "service heater" light that was coming on when the heater kept cycling every minute or so. For those of you trying to diagnose this problem, the key is the intake water temp. When the spa or pool is 55 or 65 degrees, the heater works perfectly because the outlet temp is maybe 85. You think everything is OK and it has fixed itself. But when you get the pool up to 85 or above, the outlet temp starts getting near the point where the safety temp switch kills the heater. If the thermostat is working, it mixes the super hot water out of the heater with some cool water to keep it under 120 degrees. If the thermostat isn't working, the heater just turns off, then tries again, then turns off, etc.

This was probably related to the pool chemistry which had a horribly high pH for quite some time before and after my purchase of the house (the hole in the piston was probably corrosion related). I only added acid in small amounts as recommended. That might be a good practice for long term maintenance but when you are dealing with pH so high that Leslie's can't give you a read, then you need gallons of muriatic acid. I'm fine now and I expect that things will be OK from here on out.

Thanks again for your help everyone!

Nick in Palm Springs

I have a sta rite pool heater model Src 333. The proble is that the heater starts and when the heat starts blowing from the exhaust it shuts down after 6 seconds. I try a new stack flouit sensor and a new ingnaiter it still does the same think .thank you

Hi. I was reading all the comments and tried to first replace the stack flue sensor. This didn’t fix the issue of the heater shuting itself off after 10-15 seconds And turning back on. Then I replaced the thermistor and still my heater was still doing it. Today I replaced the thermal regulator and now the Service heater ligh turned off and instead the service system light turned on first then the heater made a loud clicking noise several times and shut off. And at the same time it shuts off the temp shoots up to about 128 and then slowly drops back down to 70 and that’s it. Doesn’t even go back on. Can someone help me figure out what’s wrong prior to me replacing the entire heater part by part. Thanks

Salt water pools/spas are notorious for high pH issues. Plastic stem on bypass assembly on these heaters are not uncommon to fail after a few years especially on spas with higher sanitzer levels. If heater is cycling on and off and getting a HS error LED indication on underside of control board, check the bypass and thermo governer espesially if more than a few years old.

Thank you all - I had the same problem where "service heater" light that was coming on when the heater kept cycling every minute or so Max-E-Therm 400 gas heater . I took out the thermal regulator and it was all rusty and just need replacement. I tested the heater without the regulator and it worked perfectly so I went and bought " StaRite Pool Max-E-Therm SR-200, 333, 400 Water System Thermal Regulator Kit (incl Spring Clip) 38000-0007S"

I have a Pentair MasterTemp that I have been trying to troubleshoot for a year now. It calls for heat, heat starts for maybe 5-10 seconds, then stops, temp raises rapidly to 124 then slowly back down to 75 and cycles again doing the same thing over and over again. So far I have replaced the thermal regulator, igniter, thermistor and the bypass valve in the manifold.

Today, I did a bunch of troubleshooting.

1. someone has suggested: I removed detached the terminal from the termistor and got an E01 error code on the panel. I connected my old termistor and got a reading of 85 degrees. When I hold it, the temp slowly went up to 90. I then reconnected the terminal on the new terminstor and got 75 (I guess that's the water temp).

2. When problem started happening last early last year, one of the thing I did was replaced a broken Jandy check valve between the heater and chlorinator. I also noticed that the flap wasn't opening even at 3450rpm and 20-25psi. Although, there's strong water coming out of the 2 return lines. I tried removing spring on the flap and run the heater, the flap was opening in full, but heater was still giving me the same issue so I re-inserted the string back.

3. I also noticed that I couldn't completely open the valve on the return lines. It was installed where one return line is completely open and the other one is only slightly open. So, I opened the 3-port valve and adjusted it where the 2 return lines are fully open. I run the heater and this time it did something different. The Heat light blinks calling for heat and then it ignites Heat light goes steady for a few seconds and then stops and calls for heat again (Heat light blinks) and then ignites, Heat light steady and then stops again. It kept doing this several times and then sometimes the temp will start counting up rapidly and slowly counts down to the current temp and cycles again.

Note: when the opened the manifold last winter to replace the bypass, the manifold and the heat coils have no signs of scales. I only found 1 small stone stuck inside where the bypass is. So I thought that was causing the problem.

In case there is blockage in the heat exchanger, how do I fix that?

Thanks for your advise.

Here are the video links. 1st one is the initial issue. The 2nd is after modified the 3-port valve to the return lines.

https://youtu.be/OaYfnEbjAFU

https://youtu.be/OLxQI4lA1eg

By the way, no error codes in front and no led error light indicator on the back as well.

James, from TFP (Trouble Free Pool) noticed on my 3-way valve going into the heater. The valve was allowing the water to go into the heater and also the bypass at the same time therefore resulting into a low flow into the heater.  As soon as I read his reply I thought right away it all make sense.  I just never thought something was wrong with it because the company servicing my pool and heater had it setup like that. Bought the house 2.5 years ago. I should've tried harder to learn how the pool works. This is a very rewarding learning experience for me. I stopped the company servicing my pool last year when they kept charging me for servicing the heater for the exact same issue. I just didn't trust them anymore.  So I heed his advise although the flapper in the check valve still doesn't open completely, the heater started working again. I let it run and the temp slowly went up from 74 to 77 in just an hour without stopping. So I'm very happy. I cannot thank you enough for all the help. I'm so glad I didn't have to buy additional parts.

Paul, your post just saved me a ton of work and worry. I had exactly the same thing going on, just adjusted my valve to "force" the water through not just "let" it and it's all set! It was working before as I "fixed" it a couple weeks ago... by turning the gas on, hah! But have been having pressure issues otherwise since (haven't been using the heater and closed valves going in/out of the heater) so maybe now, closing that one valve I have to force the water through the heater, is more needed... Anyways, thanks a million!