14M2 locks up when set point exceeded

symbol setpoint = b0
symbol sensor = C.4		;thermistor
symbol temp = b1			;8 bit analoge of temperature
symbol longloop = b3
symbol loopperiod = b9
symbol recent = b4		;temperature stored recently
symbol earlier = b11		;not used
symbol lowdiff = b2		;units temp is below setpoint
symbol gain = b7			;additition added to duty period over time
symbol shortloop = b5		;loop that creates duty cycle
symbol heat = B.1			; FET turns on load
symbol duty = b8			; duty period withing cycle

Main:
	Let setpoint = 150
	let loopperiod = 50
	readadc sensor, temp
	let gain = 0
	let recent = temp

testemp:
		if temp > setpoint then		 	 
		 	goto oneoff				;if too hot switch off
			endif
	if temp <= recent then				; if cooled since last store increase gain
		let gain = gain +1
			endif
	if gain = 0 then					; if gain already zero avoid subtracting from it
		goto skip
			endif
	if temp = setpoint then				;if reached setpoint then reduce gain
		let gain = gain - 1
			endif	
skip:	
	for longloop = 1 to loopperiod		;approx 50 second loop stores current temp at end
	readadc sensor, temp					
debug
		if temp > setpoint then		 	 
		 	goto oneoff				;if too hot switch off
			endif
	
	let lowdiff = setpoint - temp			;find differential				
	 						
	let duty = lowdiff * 3 + gain			;duty period proportional to differential plus gain
	
	
	for shortloop = 1 to 30				;approx 1-second loop for duty cycle
	
		if shortloop > duty then gosub oneoffa	;if iterations exceed duty switch heat off
	
		if shortloop <= duty then gosub oneon	;if iterations <= duty switch heat on
						
	debug
		pause 10
	
	next shortloop
			if longloop = loopperiod then	; at last iteration oflong loop store current temperature
				let recent = temp
						endif
	next longloop
		goto testemp				;go to start and measure temperature	
	

	
oneoff:
	low heat
	wait 2
	goto testemp

oneoffa:
	low heat

		return

oneon:
	high heat
		return