Mastertemp troubleshooting, voltage to gas valve seems low.

[Coldfusion]

Hi everyone, new guy here.

I moved to the Austin area recently and bought a house with a pool, learning things! The pool has a master temp 400 heater that is not working and I could use some advice. First a breakdown:

1 - Not sure the age of the heater (I need to look up the SN) but it is several, maybe more, years old.
2 - Power on seems OK, I jumpered the line from the intellecenter to keep the heater powered on (bad wire between the firemans switch and intellecenter relay, different problem).
3 - When I turn the heater on there are no error codes (or error LEDs on the back of the board) I made sure the water temp setting is above what the heater is reporting the water temp.
4 - The heating light flashes and from what I can tell the system tries to open the gas valve, cycle a few times and service heater led lights up. No other led's on the back of the board light up, no error codes.
5 - No noticeable gas smell when the valve should be open, also no movement on the gas meter.
5 - Checking voltages I found something that seems wrong, the signal from control board to gas valve (see pic) hits 6v for a about 5 seconds then drops back to zero.
- I think this 6v (AC) should be 24v to trigger the valve
- Measurement was taken with and without the wires hooked to the gas valve
- I have tried 2 different control boards and 2 different ignition control modules, same result
6 - Only other thought is the valve, measuring across the terminals, switch "ON" there is a dead short between the terminals switch "OFF" there is only about 280ohm. Did a short in the gas valve maybe damage the control boards?
7 - Even if the valve is bad, unless the controls are damaged I would think it should be getting 24v sent to the valve.



Suggestions?
And Thanks!

 

[1poolman1]

Hi everyone, new guy here.

I moved to the Austin area recently and bought a house with a pool, learning things! The pool has a master temp 400 heater that is not working and I could use some advice. First a breakdown:

1 - Not sure the age of the heater (I need to look up the SN) but it is several, maybe more, years old.
2 - Power on seems OK, I jumpered the line from the intellecenter to keep the heater powered on (bad wire between the firemans switch and intellecenter relay, different problem).
3 - When I turn the heater on there are no error codes (or error LEDs on the back of the board) I made sure the water temp setting is above what the heater is reporting the water temp.
4 - The heating light flashes and from what I can tell the system tries to open the gas valve, cycle a few times and service heater led lights up. No other led's on the back of the board light up, no error codes.
5 - No noticeable gas smell when the valve should be open, also no movement on the gas meter.
5 - Checking voltages I found something that seems wrong, the signal from control board to gas valve (see pic) hits 6v for a about 5 seconds then drops back to zero.
- I think this 6v (AC) should be 24v to trigger the valve
- Measurement was taken with and without the wires hooked to the gas valve
- I have tried 2 different control boards and 2 different ignition control modules, same result
6 - Only other thought is the valve, measuring across the terminals, switch "ON" there is a dead short between the terminals switch "OFF" there is only about 280ohm. Did a short in the gas valve maybe damage the control boards?
7 - Even if the valve is bad, unless the controls are damaged I would think it should be getting 24v sent to the valve.

View attachment 534754

Suggestions?
And Thanks!

Check all your wiring for rodent damage. Check voltage with the wiring removed from the valve. It may be the valve itself.

 

[Coldfusion]

I do not see any obvious signs of critter dmg, at least not in the wires from the control board to the valve.
I tried pulling the wires off the valve and testing the voltage at the control board pins, still only seeing about 6v.

Two control boards, same result, maybe both are damaged. Should the valve show near zero resistance when the switch on the valve is in the "on" position? That seems like a power to ground short setup the first time the control board tries to apply the voltage, I would think it would trip the fuse, but maybe it just damages something in the control board.

 

[swamprat69]

I think that this is the manual for your heater https://www.pentair.com/content/dam...p/manual/Manual-MasterTemp-472592-English.pdf The wiring diagram and ladder diagram are on pages 40 & 41. The 24 volts to the gas valve consisting of a 24 volt "hot" leg and a 24 volt "ground" leg from the transformer do not originate from the control board ( they pass through it by way of circuit board traces and circuit board connections ). The original 24 volt hot ( the switched part of the circuit) signal for the gas valve originates at the "VAL" terminal of the Fenwal ignition control and passes through the control board and the AGS switch before reaching the gas valve. If you have 24 volts between VAL and GND on the Fenwal, you could try tracing with one meter lead on GND and tracing to the VAL connection on the circuit board and through the AGS connections to see where you are dropping the voltage. Any deterioration of the ciruit board traces, connections/pins, wiring or contacts in the circuit can be the cause of a voltage drop.