Pentair Mastertemp 400 SFS error, need help

[Zizzam]

Hi all, let me start by saying I've spent hours researching and reading up on the issue I'm having with my heater but I have a few questions on how to best proceed (I'm handy enough but pool equipment is new to me). We are in a new home and had the pool opened about 2 weeks ago. We've been using the mastertemp 400 heater to heat the spa without issue until a few days ago when the heater kicked on, ran for 3-5 minutes and would shut off. I started looking into it, got the top off and found the SFS error code. I tested the stack flue temp and it is rising up over 450+ hence the heater shut own.

The interior of the unit looks pretty clean, no major wear and tear. I checked the air intake and output and they both look OK to me and have cleaned out the pool filters to ensure sufficient water flow. I also removed and tested the thermal regulator and while it has a bit of green corrosion is is functioning as expected running under hot tap water.

After reading the forums it sounds like I likely have an issue with a sooted or calcified heat exchanger. My issue is how to figure out which to investigate? I've looked but I dont really understand what I should be looking for with a sooted exchanger before I go remove the manifold to check for calcification? Appreciate any guidance and I can post pictures if that's helpful. Thank you!

 

[Zizzam]

Reading more of the past posts, I will check the manifold bypass valve today and post some pics

 

[ajw22]

Welcome to TFP.

You can't see the heat exchanger coils without opening the sealed burner pot.

The Sta-Rite heater has all the same parts as the MasterTemp in a round case...

Pentair MasterTemp Heaters - Further Reading

www.troublefreepool.com

 

[Zizzam]

Awesome thank you! I'm excited to disassemble this bad boy (I think?!)

 

[1poolman1]

Before you completely tear that heater apart (and you have to to get into the combustion chamber where you will see nothing) just take off the manifold and you will see into the heat exchanger tubing as far as you will ever be able to. We only open the combustion chamber to replace the heat exchanger, and then the heater is usually too gone for that to be worth the money.

If you pull one of the very bottom manifold bolts and water comes out, the heat exchanger is leaking. That indicates that it really is new-heater time. A complete heat exchanger, depending on the btu capacity of the heater, starts at around $550.00 for the smallest and goes up from there. A complete kit, which includes all the parts necessary for the job can be upwards of $2000.00. That's if there is no manifold and control parts damaged

The manifold bypass is right inside and the manifold has to be removed to replace it, anyway

 

[Zizzam]

Ok an update, first off, I found out the heater is only about 2 years old, the internally all look pretty good. I took the manifold off and everything looks just fine. I have a replacement thermal regulator coming in the mail today since mine LOOKS a bit corroded but under hot water it seems to be functioning as expected. So, pool filters completely cleaned, all air intake looks fine, exhaust looks clear, heat exchange looks fine from the manifold side... what else can I check? The only other thing I've read that could cause the SFS error is a faulty board? Again when I test the stack flue temp it does climb up over 450+ and that's when the system errors out. Thanks again all for your contributions, I really appreciate it

 

[ajw22]

Did you open the manifold and examine the bypass valve?

I would replace the bypass valve as well as the thermal regulator even if they look good.

Basically the high flue temperatures indicate the water is not absorbing the BTUs and the heat is coming out the exhaust which is over temping it.

That is usually a water flow problem with insufficient water flow through the heat exchanger. The thermal regulator and the bypass valve are the two mechanisms that control the water flow internally in the heater.

Measure the exhaust temperature using an IR thermometer. If it is truly high then it is not the board or a sensor. It is a water flow problem.

 

[Zizzam]

I dont have an IR thermometer but I will get one, I know the exhaust is HOT just from feeling it. I will check out the bypass valve, thank you!

 

[JamesW]

Do you have an external bypass?

Can you show your whole system?

 

[ajw22]

Do you have an external bypass?

Can you show your whole system?

Welcome back.

 

[Zizzam]

Ok, opened the manifold, bypass valve is in place and seems functional. I pulled it out and it is able to move under compression. You think I should replace it anyways?

 

[Zizzam]

No external bypass (I dont think?), here's my whole system. I only have two modes, pool and spa, the valves move automatically. Everything has been working fine for weeks, pool is clear, water flow to the spa seems OK

 

[ajw22]

Ok, opened the manifold, bypass valve is in place and seems functional. I pulled it out and it is able to move under compression. You think I should replace it anyways?

I see some corrosion on it.

You are that far into the system. I would not want to need to go into it again for want of a $46 part,

 

[Poolster223]

the amount of green on the pipes inside your heater lead me to believe you have a water chemistry issue please keep your water properly balanced. Most pool equipment can me damaged by improper water balance. Other than that your thermal regulator (last pic) looks like it is bad

 

[Poolster223]

the amount of green on the pipes inside your heater lead me to believe you have a water chemistry issue please keep your water properly balanced. Most pool equipment can me damaged by improper water balance. Other than that your thermal regulator (last pic) looks like it is bad

im also seeing an SFS code comes from A Sooted exchanger or a calcified exchanger you've measured the air temperature of the air by pressing and holding the pool on or spa on buttons depending on what mode your heater is in and it will switch the display to air temp instead of water. check the SFS sensor with a multimeter set for MegOhms if the heater is set for 77degrees then the ohms should read 3.8
if not its a bad SFS sensor

 

[JamesW]

Check the salt cell to make sure that it's clean.

Try running with the thermal regulator removed to see what the SFS temp is with no thermal regulator.

 

[Zizzam]

Good idea, I'll check the salt cell.

I've replaced the thermal regulator and the SFS now (I had ordered one just as a backup). I have everything back together now it ran longer than before but eventually errored out but now I get a HLS error instead of SFS.... The pressure in the spa seems fine coming from the jets, I will say the water coming is luke warm, not hot like it was when the heater was working properly.

 

[ajw22]

Good idea, I'll check the salt cell.

I've replaced the thermal regulator and the SFS now (I had ordered one just as a backup). I have everything back together now it ran longer than before but eventually errored out but now I get a HLS error instead of SFS....

You can test the HLS the way James says below.

The pressure in the spa seems fine coming from the jets, I will say the water coming is luke warm, not hot like it was when the heater was working properly.

Heater outlet temperature rise will depend on the water flow rate. Slower water flow will have greater outlet temperature since the same BTUs go into less water volume.

Changing the pump speed can vary the return temperature from just warm at high RPM to very hot at minimum flow for the heater.

For example, a 400,000 btu/hr heater with an efficiency of 84% transfers 336,000 btu per hour to the water.

At a minimum required flow of 40 gpm, there will be 2,400 gallons of water (20,000 lbs.) that receives the heat.

Each btu raises the temperature of one pound of water by one degree Fahrenheit.

336,000 btu into 20,000 pounds of water is 16.8 degrees of temperature rise (336,000/20,000).

So, the maximum temperature rise you should ever have is 16.8 degrees Fahrenheit.

As shown below, higher flow results in a lower temperature rise.

• 40 gpm = 16.8 degrees temperature rise
• 50 gpm = 13.44 degrees temperature rise
• 60 gpm = 11.2 degrees temperature rise
• 70 gpm = 9.6 degrees.
• 80 gpm = 8.4 degrees.

Heater Maintenance - Further Reading

 

[Zizzam]

Thank you all for the input. So now the SFS temp hits about 375 and holds steady but after 5 minutes or so the system errors HLS, the heater kicks off for a minute or so then turns back on until the HLS error comes back. I'll check the salt cell tomorrow and test the HLS sensor with a multimeter

 

[JamesW]

You can test the HLS using a multimeter. It is a 10K thermistor.

The HLS is just an On/Off switch and not a thermistor.

You can test it in a cup of hot water to see at what temperature it goes from closed to open.

The high limit switch (HLS) opens if the heat exchanger outlet temperature goes above 135° F (57° C).