Another Mastertemp 400 cycling

[hambone]

Need help diagnosing.
Long story…
My mastertemp 400 sprung a leak in the exchanger about 2 years ago. I patched it with JBweld and it held until a week ago when my heater stopped working as the patch failed.

I bought a new heat exchanger, and when I went to replace it, noticed the combustion chamber was rusted out as well as the lid…. I ordered a new one and was informed they are 7 months backordered!!! Since i bought the 800 buck exchanger, i am in too deep and should have bought a new heater…. Anyway…. i repaired the combustion chamber and lid with steel sheet and high temp mortar to get through the season but now my heater short cycles. I bought all new sensors and it still short cycles. i believe i may have either a grounding issue, or flame sensor voltage

The heater does light, first time for 30 seconds, then 5 seconds several times before locking out…. I checked the flame sensor voltage and its barely below 1…. With my metal hack, im wondering how to test grounds or voltage? Im at the point of about to try buying a new fenwal.


Is there a way to bypass the fenwal to make sure its bad? How do you check ground? I pull the wire from the valve and it shuts off… flame sense voltage is around 1…

What do i try next?

 

[ajw22]

Welcome to TFP.

Have you replaced the igniter which senses the flame in the MasterTemp?

Read Heater Flame Sensing - Further Reading

 

[hambone]

Welcome to TFP.

Have you replaced the igniter which senses the flame in the MasterTemp?

Read Heater Flame Sensing - Further Reading

Yes, i put the new igniter in- it came with the heat exchanger. On the Fenwall FC leads, it tests it reads around 10 uA dc while hot. The old igniter was lower. This morning i took the thing apart and ran a ground wire from the burner bolts under the blower, the blower bolt, then to the fenwall ground - read that its a known issue.

When i unplug the heater and plug it back in - it runs for about 30-60 seconds, and gets to 305 degrees…. Once it shuts off it goes 5 seconds on, ~30 seconds off - all day.

When I pull the wire off the gas valve when its running it stops.
Not sure what else to try or test - no error codes

 

[ajw22]

You check the thermal regulator and the bypass valve?

Try running the heater without the thermal regulator.

 

[hambone]

You check the thermal regulator and the bypass valve?

Try running the heater without the thermal regulator.

Yes, new thermal regulator (tested it in my sink ) and the bypass valve also new (came with exchanger). I also ran pool without filter and at various flows with the variable speed pump.

I also tried jumping each of the devices on the manifold individually as well as the airflow gauge - each of these trigger a warning light on the board.

Im tempted to buy a fenwal on amazon that i can return or a board. Sorta stuck since i dont know how to test gas pressure.

I will try without the regulator when i get home in a couple hours.

 

[hambone]

Just tried without thermal regulator in, now it runs for 25 sec on then 30 off…. Which is better in that it is heating (was 78 earlier and is now 82) in time for teenagers prom party tonight.

 

[ajw22]

You have an internal water flow issue.

Things are overheating inside the heater.

I would look at how you installed the heat exchnager and the manifold.

It is not a Fenwal problem.

 

[hambone]

You have an internal water flow issue.

Things are overheating inside the heater.

I would look at how you installed the heat exchnager and the manifold.

It is not a Fenwal problem.

That is a relief. I will check that out. What to look at in particular? Bypass valve? There didnt seem to be anything you could get wrong or backwards.

 

[ajw22]

That is a relief. I will check that out. What to look at in particular? Bypass valve? There didnt seem to be anything you could get wrong or backwards.

The heater is an engineered machine that puts out a set amount of heat. The designers balanced how much of that heat is absorbed in the water through the heat exchanger, how much is lost through the casings, and how much heat should go up the exhaust. The safety sensors are set to trigger if it does not see the right balance of heat.

I suspect your various repairs have upset the designed balance. Your combustion chamber repair may be letting too much or too little heat through the sheet metal you used. The sheet metal may be a different thickness and have a different amount of heat transfer then the original sheet metal.

You have to fully understand how the heater operates and the heat transfers happening and which safety sensor is shutting down and cycling to know what is going on. The heater theory of operation is described in the Installation Manual.

Pentair MasterTemp Heaters - Further Reading

www.troublefreepool.com

 

[hambone]

The heater is an engineered machine that puts out a set amount of heat. The designers balanced how much of that heat is absorbed in the water through the heat exchanger, how much is lost through the casings, and how much heat should go up the exhaust. The safety sensors are set to trigger if it does not see the right balance of heat.

I suspect your various repairs have upset the designed balance. Your combustion chamber repair may be letting too much or too little heat through the sheet metal you used. The sheet metal may be a different thickness and have a different amount of heat transfer then the original sheet metal.

You have to fully understand how the heater operates and the heat transfers happening and which safety sensor is shutting down and cycling to know what is going on. The heater theory of operation is described in the Installation Manual.

Pentair MasterTemp Heaters - Further Reading

www.troublefreepool.com

Thanks for the detailed responses. I am really trying to understand which sensor is shutting down to get an idea of what is going on. The manual is great to show why an error occurs, but i guess I need to research the nuances of what is being monitored and triggered in “non-tripping” an error. For example what is in the design is telling the gas valve to close when the flow or temp combination is outside operating ranges but not enough to throw a code.

It is unfortunate that I cant source a new combustion chamber and lid.

I guess I will just buy a new heater and have all the spare parts…. Maybe try to part it out to sell on ebay or keep them. This is my 4th heater in 15 years - all of which were used. The first failed due to tab feeder, second failed due to freeze, third was not having a sacrificial anode when I switched to salt, and this one had a pin hole leak (not sure why). This forum helped me on every single one of my issues despite the fact I never posted until now… so thank you for the assistance.

 

[ajw22]

For example what is in the design is telling the gas valve to close when the flow or temp combination is outside operating ranges but not enough to throw a code.

The Ladder Diagram below shows the safety logic. If any of the safety switches open it drops the 24V that powers the gas valve open. Really very simple.

Have you had the top cover open and the board flipped over so you can see the diagnostic LEDs? If you are quick you should see an LED blink ON then OFF for the safety that is opening and then resets.

If you buy a new MasterTemp heater then the latest version has a new diagnostic messaging system that displays on the panel.

Pentair MasterTemp Heaters - Further Reading

www.troublefreepool.com

The ladder diagramn

 

[hambone]

Thanks for this. I dont know whats going on, but the heater ran f

 

[hambone]

Update - in case someone else goes down this journey.

I finally determined that I was not getting any flame signal from the igniter to the Fenway and it was likely due to grounding issues (or lack of ground) related to the rust or repair of rust on the lid. I finally found a used lid and installed it and now the unit works fine.

Again - to recap….this unit was cycling forever with no codes- the exchanger had sprung a leak and the tub had rusted. I tried to repair the tub after getting a new exchanger but I had cycling issues.

I rigged a ground wire between the various bolts of the ignition but the lid itself was rusted and I had reinforced it.

I hope this helps someone. I appreciate the help!