Mastertemp 400 Heat Exchanger replacement

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jpcdmd

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Nov 7, 2007
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Problem with my Pentair Mastertemp 400 NG heater. It will fire up but only run for a few minutes before shutting down, and Service Heater light comes on. The SFS led is lit. I've replaced the stack flue sensor, the thermostat, and the thermistor. Finally got a pool technician to look at it and he said there's a problem with the heat exchanger. He said they do not service that part due to liability issues, and that I could either clean or replace the heat exchanger on my own or replace the entire heater.

So I'm trying to figure out how difficult it is to replace the tube coil assembly but I can't find any tutorials anywhere. Does anyone know how to do this? I can sling a wrench, but prefer to see a how-to video or guide beforehand.
 
It can be done and is a pain in the rear, my opinion. How old is the heater? Ive seen something done to clean the heat exchanger using compressed air but I would not recommend a homeowner do it. Usually when something like this comes up, the cost of parts and labor to go thru the hassle to replace the heat exchanger always leads to just replacing the entire unit.

Here is one place to buy the tube sheet assembly. Pricey. http://www.parts4heating.com/Pentair-77707-0234-Tubesheet-Coil-Kit-400K-Pool-He-p/77707-0234.htm
 
ps0303 said:
It can be done and is a pain in the rear, my opinion. How old is the heater? Ive seen something done to clean the heat exchanger using compressed air but I would not recommend a homeowner do it. Usually when something like this comes up, the cost of parts and labor to go thru the hassle to replace the heat exchanger always leads to just replacing the entire unit.

Here is one place to buy the tube sheet assembly. Pricey. http://www.parts4heating.com/Pentair-77707-0234-Tubesheet-Coil-Kit-400K-Pool-He-p/77707-0234.htm
Click to expand...

The heater was put into service in 2008. I replaced the top cover and motherboard about 5 years ago, and recently replaced the thermostat, SFS, and thermistor (about $150 total). I feel those are the most commonly replaced parts so if I can replace the heat exchanger without much problem I should be able to get at least a few more years out of it and save about $1000, as opposed to dropping over $2k for a new heater only to have to replace more parts in 2-3 years.

There's gotta be a tutorial somewhere on the web :confused:
 
I found a video that should work. Its for a Sta-rite heater so the case is different but I think the guts are the same as the Pentair Mastertemp. Doesn't look too difficult. There's a Part 1 and Part 2 videos. I think I will choose to replace the coil assembly rather than just clean it since I do have a SWG and with my luck I'll develop a leak in the thing within days after reassembly if I just clean it. I'd rather have a new part. Sunplay has it for just under $600 shipped.

https://www.youtube.com/watch?v=w5fEnagoRbU
 
Good luck. Sta Rite and Mastertemp are the same units just different outer cases.

Cupro nickle isn't worth it in my opinion.

Sunplay is selling it at pretty much cost. I can't see how these internet companies can sell so cheap and give free shipping.
 
Unless it is leaking, there is little reason to replace the exchanger, other than scaling (bad water chems). You can clean it with a brush, or the compressed air method. Just be aware of the mess it will create. Do it in an area that can tolerate the mess, and wear some kind of breathing protection.

A bit about the lights on the back of the board. The light(s) will come on when that particular safety switch or sensor opens, or gets information that is not conducive with what would be proper operation. It is NOT necessarily telling you that that part has failed. This should be taken into consideration when diagnosing the heater. This is in no way saying that OP did or didn't replace parts that he shouldn't have.

I see lots of threads where the customer sees one light come on, and starts to replace several parts that appear to be bad, but not necessarily the cause of the heaters problem. And the "Pros" here, myself included, fail to address that. Pentair can take part of the blame here, for vague troubleshooting info, but the customers have come here, and are asking for help, from us. So, if i am wrong, and some of you have addressed this, sorry, but keep in mind you may have to be a broken record, you may have to explain this more than once since OP's don't always read all the relevant threads before they decide to post theirs. And putting it out there helps the ones who have not yet started a thread and are looking to save some time and money too!

There, i'm done...
 
It is hard sometimes to wade thru all of the clues given by a poster. And you make very valid points Pool Clown. As I stated, I've never replaced a heat exchanger especially on one of these nor do I recommend it. Maybe the OP will find something along the way that will explain the problems he is having.

I wonder if there is water in the can? I say/think that alot on these units.
 

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The heater will run for a few minutes and then shut off. The exhaust feels VERY hot. I tried holding the buttons down to read the exhaust temp but it read nothing. I also tested the SFS sensor with a multimeter prior to replacing it and could not get a reading so I assumed it was bad. After replacing the SFS I started getting the AGS led, and not the SFS any more. It was then that I replaced the thermostat and finally the thermistor, and now the SFS light is back on. That is when I gave up and called the tech, and he confirmed that its getting too hot and shutting off. He didn't actually recommend replacing the coil assembly, just cleaning it with a brush. It was my idea to just replace it since I would already have the unit apart. I think at this point I will disassemble it, clean and inspect it, then decide whether to replace the coil or just close it up. It is not leaking water at the moment. I have to admit I have not been the best with regards to maintaining the chemistry and have not closed the bypass valve during the off season to restrict flow to the heater. I will do this in the future now that I'm aware of the problems that occur with the coil assembly.
 
jpcdmd said:
I think at this point I will disassemble it, clean and inspect it, then decide whether to replace the coil or just close it up.
Click to expand...

Take and post some pics of the exchanger when you get it apart.

For the future: Bad stack flue sensor most times wont let the heater even start because it is giving an incorrect temp (to the board) to start with. If the heater runs and shuts off displaying SFS, sensor is probably doing its job correctly and you have a heat transfer problem (sooting).

Bad thermistor, same thing, or will start out with a close temp reading but display will rise un-proportionately in about a min to a ridiculous temp say >150 degrees.

Bad thermostat (thermal regulator) will show you visually that it is bad (rust, corrosion, and/or blue-green color).

I have also seen this when the igniter is not giving, or the fenwal is not seeing a flame rectification. But if you are getting SFS and feels hot it is probably a heat issue and not Fenwal. Would like to know SF temp to confirm your problem. for review, hold pool or spa, whichever is illuminated, for 10 seconds, board should display stack temp.
< 250 real low
250-290 low
290-350 target
350-500 too high
 
I had a good one today. Sta Rite would run for a bit and shut off on HLS. Looked at the thermal regulator, pretty bad shape so I replaced it. HLS still came up. Replaced the high limit and it still came up. Bypass was what I could feel in good shape. I pulled off the manifold and inside was a ton of **** from when they did some work on the pool finish. Homeowner was back north and the neighbor was there and he confirmed a little over a year ago the pool finish had some issues and a company came out and did some grinding and patching. Well apparently some of the uncleaned up finish ended up in the heater. I also had to flush out one tube of the heat exchanger as it was clogged. That was a good one.

Just passing on some info on a lesson learned.
 
I'm not sure but it was annoying to say the least. Just one example of how you can be lead down a rabbit hole and it's not what you thought the issue was. This is also a great example of how hard to can be to provide help on a forum as you really needed to have hands on with this one. Even pulling out the thermal regulator didn't expose the problem.
 
jpcdmd said:
Problem with my Pentair Mastertemp 400 NG heater. It will fire up but only run for a few minutes before shutting down, and Service Heater light comes on. The SFS led is lit. I've replaced the stack flue sensor, the thermostat, and the thermistor. Finally got a pool technician to look at it and he said there's a problem with the heat exchanger. He said they do not service that part due to liability issues, and that I could either clean or replace the heat exchanger on my own or replace the entire heater.

So I'm trying to figure out how difficult it is to replace the tube coil assembly but I can't find any tutorials anywhere. Does anyone know how to do this? I can sling a wrench, but prefer to see a how-to video or guide beforehand.
Click to expand...
Hi, I have the same problem with my mastertemp 250. Did you have any issues with taking apart the canister to access the heat exchanger?
 

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