Mastertemp 400 SFS overheat

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webber498

Member
Jan 30, 2023
23
UK
Hi all,

I have a Mastertemp 400 HD (euro model as I’m in the UK) and it’s been faultless for the last 2.5 years.

Recently it started to cut out, I did as much reading as I could online and found that it was because my stack flue temp was reaching 480.

I checked water flow, replaced the internal bypass, replaced the thermal regulator, took the manifold off to check for any calcification of the heat exchanger and there were no signs of any.

With the Thermal Regulator removed it will run but the SFS temp sits at 460. If I put the regulator back in it tips it over the edge to 480 and cuts off…

I have ordered a replacement SFS sensor to try but from what I have read it sounds like my issue could be soot in the burner and heat exchanger.

I found some videos on how to remove and replace the heat exchanger but nothing on de-sooting it.

I wondered if anybody could advise on how best to de-soot it please? (If there is any way to do it without removing it all then great, but I will do whatever is needed)

I’d also welcome any other thoughts of what the issue could be if it’s not soot. I did have a look down the exhaust and it looked quite clean so I’m not 100% sure it even is that.

Thanks in advance

Adam
 
Soot is virtually a non-issue on a MasterTemp/ Max-E-Therm as they
have metered air and fuel. May be possible with very low gas pressure, but very unlikely. Usually the heater just won't light in that condition.
May be able to tell by removing the blower and viewing the combustion chamber.
If sooted, the only way to remove it is to remove the heat exchanger and wash it off. That's a complete teardown of the heater, a lot of work.

Still could be a waterflow issue.
 
Thank you for the response, appreciate it.

I’ve got a flow meter on the water feed and it’s showing around 160LPM so around 42GPM which I think is enough isn’t it? The water flow has always been at that speed since the heater went in.

I’ll replace the SFS sensor when that arrives. If that doesn’t work I’ll have to tear down and check for soot I guess. Beyond that could it maybe be the control board?
 
Have you checked the bypass valve?

It is not the board. The board does not effect where the heat goes.

The heater generates a fixed BTU of heat. The heat either gets absorbed by the water flow and exits the heater out the water or it exits through the exhaust. A SFS problem says the heat is not being absorbed by the water flow and too much is going out the exhaust.

There is an internal problem in the heater preventing the heat getting into the water so it goes out the exhaust.

Point an IR thermometer at the exhaust and you can confirm the exhaust temperature and if you have a bad sensor.

Pentair MasterTemp Heaters - Further Reading

www.troublefreepool.com www.troublefreepool.com

full


full
 
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Thanks AJW22, yes I’ve replaced the bypass valve in the manifold already as I had seen it can be a common fault.

I’ve got an infra red thermometer coming today from Amazon so I will test the temp and see if it gets a similar reading.

Not sure if this is relevant or a distraction but I use my heater to heat my koi pond rather than a pool. It means it is in use all year round and at lower temperatures than typical pool use (68 to 77f typically). It also doesn’t have chlorine in so the water side of the heat exchanger is looking great, no liming at all. I do wonder if the way I use it makes it more likely to soot up over time
 
webber498 said:
Not sure if this is relevant or a distraction but I use my heater to heat my koi pond rather than a pool. It means it is in use all year round and at lower temperatures than typical pool use (68 to 77f typically). It also doesn’t have chlorine in so the water side of the heat exchanger is looking great, no liming at all. I do wonder if the way I use it makes it more likely to soot up over time
Click to expand...

That should not create problems as long as you are not heating water that is below 60F.

Heater Condensation - Further Reading

www.troublefreepool.com www.troublefreepool.com
 
I put a bore scope down the exhaust to see the outside of the heat exchanger and this is how it looked…

Link

Hard to properly make out what’s going on but it looked like the veins on the outside of the heat exchanger could be a bit blocked up
 
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Are you filtering the water from the Koi pond before it goes into the heater? Also, what is the pH/TA/CH of the koi pond water?
 
Yes it is more heavily filtered than many swimming pools, it runs the water through rotary drum filters with a 40micron mesh plus bead filters with media (similar to a pool sand filter).

I did blow some low pressure compressed air through the heat exchanger when I had the manifold off to check there were no blockages and all was clear

PH is 7.5

I’ve just grabbed my spa test kit as I don’t usually test TA on the pond but it is showing

TA - 80ppm

CH is assume is chlorine? That is at 0. Even small concentrations will kill Koi so all fresh water added has to be dechlorinated and tested properly with an ultra low reading chlorine tester
 

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Here are some videos that show the process of getting into the combustion chamber and accessing the heat exchanger.

It's not fun or easy.

If the water flow is good and you are sure that the thermal regulator and internal bypass are good, then the heat exchanger is the next thing to check.

Can you show your system?

Can you pull the thermal regulator and show a picture looking into the thermal regulator hole and also a picture looking into the heater inlet?

The Max-E-Therm is the same heater as the MasterTemp, just in a different shell.



 
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Thank you for the continued help.

Here is a video of the heater firing up and SFS temp raising to ~450f but I have the thermal regulator out at the moment to allow the heater to keep working so the temp only goes that far and stays around 460-460. With the regulator in it carries on to 480f and cuts out in the same timeframe of around 5 minutes.

Video link

Here are some pictures of the set up, hard to show it all as there’s a lot going on. The heater sits outside of the main pump room

3EE8040F-AC5A-489C-A619-B87F2B8BDA19.jpeg
F22D32AE-7647-446A-B92A-B75A3DC641E8.jpeg
 
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If you have verified the water flow, the thermal regulator and the internal bypass, then I think that you probably need to check the heat exchanger and clean it if necessary.

The tubes might be clogged with scale inside or soot outside.

Can you pull the thermal regulator and show a picture looking into the thermal regulator hole and also a picture looking into the heater inlet?
 
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The SFS temp moves up in a smooth way, which indicates that the sensor is probably good.

The heat transfer efficiency can be diminished by poor exhaust gas contact with the outside of the heat exchanger or by poor pool water contact with the inside of the heat exchanger.

When you replaced the internal bypass, how did the heat exchanger tubes look?

Were they clean or clogged with scale?

Do you have pictures of the heat exchanger tubes?
 
I didn’t take a picture of the heat exchanger tubes but they were clear of any scale, they looked clean. I ran compressed air through each one of them to check for any blockage and all looked good.

I will try to do pictures down the inlet and thermal regulator hole later tonight once I’m back home. It all looked clear when I had it off though, I cleaned it up and replaced the bypass valve even though it all looked fine.

Using the bore scope down the exhaust it did look like the outside of the heat exchanger had some kind of scaling or calcification on it so I’m suspecting it may need stripping and cleaning.
 
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Once you get the heat exchanger clean and the heater is running, check the inlet gas pressure to verify that it is good static (Heater not heating) and dynamic (heater running).
 
Here is what the normal exhaust temperature should be:
  • Below 250 degrees...very low
  • 250 to 290 ..................low
  • 290 to 350.................acceptable
  • 350 to 480 ..................high
  • Above 480...................error/shutdown.
Note: HD models can be up to 75 degrees higher.

HD models use a cupro-nickel exchanger and the efficiency is slightly lower resulting in less heat transfer and more waste heat.

Pentair MasterTemp Heaters - Further Reading

www.troublefreepool.com www.troublefreepool.com
 
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