I have a Hayword H aboveground heater. It initally started the season with running for 20 minutes and then quitting. The other day the heater came on and it clicked every so often. Yesterday the heater would not come on at all. What's up? I checked the high limit switches and it showed Hz i just don't want to buy millions of parts to fix it and NO ONE will fix it. Should i just give up and buy a new heater?

Could it be the choke sticking.

if this is got the 27 hp kohler engine, I know exactly whats wrong with it , due to grass and engine oil building up in a short time under cylinder heads , it actually makes a tight ball of grass and stuff there !! this holds the engine heat and ruins the ign module that's just above it there , I put two on in one season ( tractor runs 6-10 hrs day 6 days a week ) I finally gave up I bought a Kawasaki 27 hp twin and installed it , now its run for two seasons and no problems
engaging the pto has nothing to do with it , it would cut off if you just drove it around for 15 minutes

20 to 30 minutes.
if this is a pool and spa combo system, then you are not only sucking water from spa and returning only to spa!
you have a incorrect setting of the valves. It needs to be 100% suction from the tub, and 100% return of water to the tub.

check fuel system

Start by cleaning all battery and ground connections.

this is 100% broken heat exchanger its the coils inside of heater that heats the water this usually happines from really old age or because your climate temperature is below freezing and broke the coils, i see it all the time in winter season, best way to prevent this is to run your heater for fifteen minutes every month and make sure pool equipment runs all day everyday when its really cold out you can start running system normaly after your outside temp is warmer. its better to get a new heater when this happines heat exchanger is hard to install for most tech's pretty much have to take whole top part of heater off and is also expensive part

The AO mindicates an open prover switch ,, here from Hawward site .
If the blower prover switch opens unexpectedly during operation the control will
shut down and attempt to re-light. If the switch does not close after the blower
starts the control will go into lockout with the blower running. Automatic reset is
immediate after error is corrected.

If the blower prover switch does not close after the blower starts the control will
stop the ignition trial go into lockout. The blower will continue to run. Automatic
reset is immediate after the switch closes.

Sounds like a weak thermostat control. You can use a meter to check it when the unit should be running but is not.

Problem 1: buy a system heater to keep the engine warm at night.
You can buy them at any autoparts store . You take your pick from the variety.
Place a light 100 Watt Bulb near the battery but not too close to anything else where it might burn anything.

Problem 2. Check your coolant level to see if you have the proper level. Make sure you have 1/2 antifreeze and 1/2 water if you add any coolant /antifreeze and bleed the colant system. By running the car let it cool, then turn the radiator cap or turn the bleed screw provided on some cars near the thermostat outlet. Then adding some more water and coolant etc.The tightening the cap or bleed screw. When radiator is full. Check the radiator and and remove any debris that may be keeping the air out.

Problem 3. Will get fixed because your battery won't die.

I just went through this with Lowrance. tthe LGC 2000 module on my LCX 20 depth finder "quit responding" out of the clear blue. You have to go Lowrance.com and they have some tests you can follow to see if it is a bad cable or the module itself. I had to replace the module. They charged $99 bucks plus $12.50 shipping for a new one. I bought it spring of 2008, and the unit was 3 months out of warranty when it quit working. Last season I had lower back fusion and didn't use it except for 2 times late in the season. Getting ahold of Lowrance is going to be an experience. I called twice and waited on hold over 35 minutes before I was suddenly cut off both times. I tried email too, but it took 3-5 days to receive a response. Mine broke down June 18 of this year. I started trying to get hold of Lowrance the next day. By the time all the back and forth emails with the delayed responses were done, I received my new unit on July 24. 5 weeks! with out my gps in MN. It is a short season up here as it is. I sure didn't enjoy waiting that long.