MasterTemp 400 Shuts Off

walker3733

LifeTime Supporter
Oct 8, 2010
40
San Antonio, Texas
Hi,

I have a MasterTemp 400 and it will run for a few minutes then shuts off and reignites again. I watched the back of the control board and LED 11 turns on each time the heater turns off. :hammer: Any thoughts?

Thanks,

Justin
 

Pool Clown

In The Industry
Sep 5, 2008
2,011
Silicon Valley, CA
LED 11 is the service heater light on the boards other side. Does the heater run fine for a while then turns off at a certain temp each time and start to cycle as you note? If it (the water temp) is in the 80's, check the thermostatic by-pass
 

ps0303

TFP Expert
In The Industry
Jul 6, 2011
4,029
FL
Is it U11? If so it should have the AFS letters next to it.

How old is this unit?

I would also check to see if there is water in the combustion chamber.
 

walker3733

LifeTime Supporter
Oct 8, 2010
40
San Antonio, Texas
The unit itself is only a couple of years old. It will heat up to a normal temperature, but the unit will cut on and off throughout the heating process. What is the thermostatic bypass? I can't find any mention of it in the manual.

Thanks,

Justin
 

Pool Clown

In The Industry
Sep 5, 2008
2,011
Silicon Valley, CA
Sorry, Pentair calls it the "Thermal Regulator" It is between the inlet and outlet, has castellations on it that you can slide a screwdriver blade in to help unscrew it. It is held in place with a spring, so when you get it unscrewed to a point, get your fingers out of the way as the cap will snap out with a little force.
 

walker3733

LifeTime Supporter
Oct 8, 2010
40
San Antonio, Texas
So just more for curiosity why would you think it would be the thermal regulator over the unsightly limit switch? Also can the thermal regulator be cleaned or repaired? I am wondering if may dirty or mineral deposits that would affect it? Oh and thank you so much for all of you help! :cheers:
 

Pool Clown

In The Industry
Sep 5, 2008
2,011
Silicon Valley, CA
When the thermal regulator is not regulating the the bypassing of water properly, it causes an overheating condition which trips the limit switch. The limit switch opening is (only) a symptom of the problem.
Unfortunately, the regulator is not serviceable.
 

Pool Clown

In The Industry
Sep 5, 2008
2,011
Silicon Valley, CA
Can you take a pic of it and post it here? What you are looking for would be rust, or corrosion on the spring side. On the other side erosion of the bulb, or even a cracked bulb evident by a crack that is green or turquoise in color.
 

ps0303

TFP Expert
In The Industry
Jul 6, 2011
4,029
FL
Gunked up looking. Maybe rusted pretty bad. One way to test is after you remove the regulator, screw the cap back on and then turn the heater on. Hold the thermal regulator at the opposite end with a pair a pliers and hold the regulator part over the hot exhaust coming out. You should see the regulator open as it heats up. If in a few minutes it doesn't open, it's bad. Shut down heater.

Now a word of warning, while removing the regulator, if it doesn't slide out easily, seems like it hung up on something, then the bypass is broken and hanging down in the way. They you will need to replace that and possibly the regulator.
 

Pool Clown

In The Industry
Sep 5, 2008
2,011
Silicon Valley, CA
ps0303 said:
Gunked up looking. Maybe rusted pretty bad. One way to test is after you remove the regulator, screw the cap back on and then turn the heater on. Hold the thermal regulator at the end of the opposite end with a pair a pliers and hold it over the hot exhaust coming out. You should see the regulator open as it heats up. If in a few minutes it doesn't open, it's bad. Shut down heater.

Now a word of warning, while removing the regulator, if it doesn't slide out easily, seems like it hung up on something, then the bypass is broken and hanging down in the way. They you will need to replace that and possibly the regulator.
+1 agreed.

Heater would knock a little too if the by-pass was broken. Bad therm reg may still open, just not the proper amount. Even in some cases you really have to look hard to find the problem with a regulator, cracks sometimes do not show themselves that easily.

At least for me...

My eyesight is getting worse by the day, it seems. :hammer:
 

ps0303

TFP Expert
In The Industry
Jul 6, 2011
4,029
FL
I've been fooled many times with a bad bypass on these units. Sometimes the bypass is broken but lodged in a way that it doesn't knock or bang when heating. The only way to find out for sure is to pull the thermal reg. The things you learn after banging you head on the wall many times.
 

Davegvg

LifeTime Supporter
Nov 30, 2008
345
I have had 2 thermal regulator failures in 4 years.

It happens.

I had very high TDS and they were sticking shut- same symptoms.




Uncle Dave
 

walker3733

LifeTime Supporter
Oct 8, 2010
40
San Antonio, Texas
Sorry I haven't responded in a while, I have been traveling for work. I took your advice and got the new thermal regulator kit, got the whole kit because there wasn't much price difference, installed it and everything seems to be back to normal. The hot tub heated up without incident. I would like to thank all of you for your knowledge and advice.

Regards,

Justin
:cheers:
 

towney

Well-known member
Apr 5, 2007
84
Central Florida
Having same issue of the unit shutting/cycling off at 79 degrees (friends). On the board the PS light is lit so I assume pressure switch, I cleaned the terminals and it worked for 4 days. Could this be the cause or are we still looking at T. regulator? Unit is 5yrs old and propane. Also in the manual is say make sure pressure tap is not blocked, where is that.
 

ps0303

TFP Expert
In The Industry
Jul 6, 2011
4,029
FL
A bad pressure switch won't cause it to get to cycle on/off at 79. Check your thermal regulator and see if it is all corroded.
 

Pool Clown

In The Industry
Sep 5, 2008
2,011
Silicon Valley, CA
PS is low pressure which the heater interprets as low flow, or a condition that would not let the water transfer enough heat away from the heater. So this pressure switch interrupts this before it is a problem.

Check for good flow by looking for a closed valve, dirty filter, clean strainer bskts, enough speed on the variable speed pump (if applicable), etc.

OR your pressure switch and or the associated wiring may have an issue.

If your getting the PS LED, all your heater knows (or cares) is that the switch is open. If you are getting intermittent operation you might be at the cusp of workable pressure (on again off again) flow.
 

towney

Well-known member
Apr 5, 2007
84
Central Florida
Checked TR and bypass and good. Heater will now only come on for a few seconds then off, PS and#6 LED on. Noticed on the PS the switch / float is in the up position. Flow good too. Bad PS? Service system light also on.