Spa heater keeps cycling between SPK and CFH. Has worked flawlessly for seven years. Used it two weeks ago. Just had four days of rain

SOURCE: Rheem model p-m266a-en-c digital gas pool heater runs, shuts down

CFH is call for heat not sure what spk is, but will find out and let you know.

SOURCE: The display will show CFH the SPK and then shut

Hard to say without more info. but a good place to start would be to check your temp reading as compaired to the water. If the reading is high this would cause these symptoms with no error message. This is a bad temp sensor and you will find it in the water manifold of the heater. I hope this helps and good luck.

SOURCE: pool heater is not working properly

So I assume you have pressed the button by pool to select the pool thermostat? If this doesn't work sounds like another mother board problem, or try powering down the unit a few minutes then restart. IF you haven't pressed the pool button, the read this: The heater comes factory set at 78° F. for the pool mode and 100° F. for the spa mode. If it's in spa mode it's trying to get to 100F. Using the up and down arrows,you can set the thermostats to a minimum temperature of 65° F., or a maximum of 104° F. If you desire to heat only one
body of water, the thermostat is capable of an off mode. As an example, if you only wish to heat the pool and not the spa simply depress and hold the spa down arrow, and the thermostat will lower its setting to 65° F. then go to an off mode. Here is a link to your manual :http://www.pentairpool.com/pdfs/MasterTempOM.pdf

SOURCE: I have a five year

CFH means "Call For Heat", and SPK is "Spark". It sounds like you are running out of gas.Propane tanks need to have 30% in the tank for a heater to run correctly,and after they are filled you must bleed the air out of the line.If you have Natural gas,the gas line may be too small to supply enough gas to keep it running. NOTE...gas pressure MUST be checked with the heater running.

SOURCE: When we tried to light the heater the CFH shows,

The CFH is a Call For Heat.
The SPK tells you that it is creating a spark for ignition.
The LO tells me that you are on propane.
The fact that it doesnt light tells me that either the ignitor is not sparking, or that there is no gas, or an incorrect gas supply.
If this unit is installed with flexible gas line, replace this with rigid black pipe or a larger flex line.