When power tuned on R3 is displayed momentarily then service heater comes on , blower starts but propane valve does not open and does not try to ignite.

These models require electrical power to run the blower fan.
When you connect the electrical cord, the fan should turn on, then you should be able to start / ignite the propane. if the fan does not turn on when you connect the power cord, you will not be able to ignite the propane.

should be a bleeder valve or a primer button,depending on the system, if the propane was off ,and unhooked it takes a while to refill the lines.

You didn't indicate what model heater you have, but here are some of the fault codes you might see. Could it have been GVO? You can download a manual for your exact model at www.raypak.com
BD1 Board failure
EEP Microprocessor error
FAN Blower pressure failure
FFL Flame sensing when pilot and gas
valves are closed
GVC Gas valve closed
GVO Gas valve open
HL1 High limit switch #1 open
HL2 High limit switch #2 open
IGN Ignition failure
ILO Ignition lockout - Propane units only
PRS Water pressure switch open
ROL Heat roll-out safety switch open
SNS Sensor failure, Water temp. below 36°F
or above 110°F
VNT Vent switch open

Hello
The click is either the gas valve opening or the ignitor trying to ignite.

From what you decribe,im going to say you have a bad ignitor.

If the gas valve is indeed opening,then you need igniton to light the gas,
which leads me to say bad ignitor.

Hope this helps.

I plug a Thermostat in The power line to break the power when at temp. Once I start the heater using the reset button,when temp is reached and the themo calls for heat just the blower comes on only. I have a All Pro propane 50,000 to 85,000 btu heater thanks Ron

The Pressure Regulator may be stuck, Try closing the propane valve releasing the pressure,, gently tap the regulator( on the propane inlet side) and Very Very slowly open the propane tank valve, and attempt to light

There can be a couple of reasons for this issue to occur. The first thing to check is the dsplay panel for which Service light is coming on. If it is the Service System light, then there is not enough flow of water in the system. You may need to clean your filter.

If it is the Service Heater light, then the problem is with the heater. What you can do is restart the heater and watch the display panel. If the water temp display is too high, or low, then the issue is the Thermister and it will need to be replaced. If the temps are about the same, then try and start the heater. The same issue may happen again, but that is what you actually want to happen. Once this does, take off the top two halves of the heater and turn the display panel over. There are diagnostic lights on the backside of the panel.

If there is a red light next to one of the following: AGS, AFS,
SFS, HLS, PS or THERMISTOR, then that is the item causing the problem with the heater. If you need an Owner's Manual, there is one online at the following link:

http://www.inyopools.com/owners_manual/sta-rite_heaters_max-e-therm.pdf

R3 is not one of the actual error codes, but is part of the computer system. What you can try to do is reset the computer in the heater. First you will need to turn the heater off, then turn off the circuit breaker for the heater. Wait about 15 to 20 minutes then reverse the order, the circut breaker then the heater. Try and start the heater and watch the display panel.

If they R3 reappears, then the problem is the control board for the heater and it will need to be replaced.

Sounds like low water flow. Is there a manual bypass that may be open? If not, thermal regulator may be bad, or worst case scenario, heat exchanger is blocked due to imbalance of ph/alkalinity in pool water. Good luck.

You should be seeing 120 volts to the igniter. Anything less requires either a replacement of the transformer, start relay or control module.