mastertemp 300 not heating water

[ttkt]

Hi all,
have already read lots of great information on this forum. i have a 15 year old pentair mastertemp 300 that was cycling on and off every minute or so but the water was hot when running. Up until this year it has run just fine. i replaced the thermal regulator and now the heater fires and stays on, but the water is not hot enough. I looked inside the thermal regulator port and it seems the bypass valve is missing. see pic. I think when I removed the old one that had been in there for 15 years I must have broken off the valve. It was completely shot and not that easy to get out. With the new thermal regulator in-place, i checked the output temp by holding in "pool" button and it only gets to around 210 when pool temp is set to 84.

If i understand correctly, I can see how a missing bypass valve would deliver unheated water since the input and output are mixing ahead of the heat exchanger, but i don't understand why the output temp would only be 210 and not higher with lower flow through the heat exchanger from the missing bypass valve. i have not looked under the panel yet to see if any lights are on, but there are no error codes from the front display.

should a new bypass valve fix my issue ? i wonder if it's worth the trouble on a 15 year old heater. thanks for any advice


s

 

[JamesW]

You need the bypass.

Once you fix the bypass, check how much gas gets used in 1 hour from your gas meter.

It should be 300 cubic feet per hour.

 

[ttkt]

.... just found the broken off valve stuck in input of the chlorinator !

 

[JamesW]

How much flow do you have?

Your stack flue temperature sensor might be going bad and providing low temperature readings.

 

[ttkt]

I guess I'll try to replace the bypass valve. not sure how to measure the flow but it seems fine. pump running full speed, no external bypass. filter is clean. three-way valves fully open to pool-side.

thanks for your input !

 

[JamesW]

If the gas usage is low, check the gas pressure.

 

[ttkt]

just ran it again after removing the broken valve from the chlorinator input which should have improved flow through system. started heater and it fired, only to shut off after less than one minute with E05 error. Tried it again and ran fine. after 5 minutes of heater on and set to 85, output temp was around 235. not sure if this should be higher by that time. water still not heated of course due to missing bypass. hopefully replacing the bypass fixes the issue, but maybe SFS needed too

 

[JamesW]

• the stack flue sensor (SFS), which shuts down the heater if the flue gas temperature reaches 480° F (249° C).

Exhaust Gas Temperature.​

While running, press and hold the On button to display the exhaust temperature (Older Models).

The new models use the Menu to get the SFS.

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.

If the exhaust gas temperature is higher then normal then water may be bypassing the heat exchanger through a broken bypass valve.

If you hold down the "pool on" button, it stays on 80, then flashes to 40, then back to 80, then the 80/40 reading and E05 indicate that the board is not getting a reading from the sensor. It's usually a bad sensor or damaged wires.

You can get an E05(open sensor) if a rat chews through the wire(s).

Pentair MasterTemp Heaters - Further Reading

www.troublefreepool.com

 

[ttkt]

after replacing broken-off bypass and sfs, heater starts and blows hot exhaust but then shuts off with sfs error after 10-15 seconds. I tested new sfs with multimeter and seems fine, and continuity of sensor wires to board is OK, no damage to wires. exhaust temp is 80 never changes, even when thermal regulator is removed. water flow is good. i did not see any leaks when removing manifold although tube ends showed some corrosion.
any ideas what to do next ? thank you !

 

[ttkt]

update ... removed control board and noticed corrosion and break in trace on back from sfs lead (pin 4). this break is very tiny and hard to see but was causing the E05. after soldering a jumper wire the heater stays on indefinitely and no error codes. so after replacing thermal regulator, bypass valve, and fixing PCB, heater seems to function as it always has but unfortunately heats slower.

Stack flue temp never gets above 255 even after 3-4 hours. the spa heated up after about 1 1/2 hours with hot water eventually, the pool heats up also but the outflow water temp never exceeds 88. so i'm guessing that the flame is weak, gas valve or pressure issue, or the heat exchanger has lost efficiency over 15 years of service.

 

[1poolman1]

update ... removed control board and noticed corrosion and break in trace on back from sfs lead (pin 4). this break is very tiny and hard to see but was causing the E05. after soldering a jumper wire the heater stays on indefinitely and no error codes. so after replacing thermal regulator, bypass valve, and fixing PCB, heater seems to function as it always has but unfortunately heats slower.

Stack flue temp never gets above 255 even after 3-4 hours. the spa heated up after about 1 1/2 hours with hot water eventually, the pool heats up also but the outflow water temp never exceeds 88. so i'm guessing that the flame is weak, gas valve or pressure issue, or the heat exchanger has lost efficiency over 15 years of service.

With a pool/spa combo pool, if the water in the spa takes that long to heat, it would be good to look into the suction valve not shutting the pool port off completely. Does the spa tend to overflow while it is being used? That's the indication that cold water from the pool is continually being pulled into the heater and it takes "forever" to get a spa to temperature.

Also, if you have a dam-wall and the water level is above it while the spa is in use the water co-mingles with the pool and the heat will flow to the cooler water in the pool.