Hi - PoolGuyNJ helped on a similar thread, seems to know these things inside and out.
I have studied how these heaters work (all of the safety interlocks and switches), but I need a better level of understanding on how to determine if I have a bad gas valve or a bad control module.
Unit was purchased used, because the exchanges internal flow diverter spring was loose and rattling (common on these). I resolved that, cleaned everything, learned the schematic and operation very well, had a licensed plumber run the gas line, and we've been enjoying it for days. A few days ago, it showed the behavior identical to another thread. "Hayward H100ID Das Heater - Cycles Once, Then No Heat" but now I am not getting ignition even when the control board sees 120v and the igniter is firing.
All of the interlocks/limit switches, etc ultimately do only 2 things:
#1 if at least flow conditions/thermostat/panel interlock met, supply 120v to the fan.. and
#2 if all conditions met, supply 120v to the control board until the thermostat opens.
Control board has only 5 connections; ground, neutral, switched line (as in #2 above) and purple out to the gas valve, and the igniter cable. Gas valve rated at 120v, purple line should be supplying 120v or close.
Here is what I am seeing:
Plug unit in. Gas line valve is open, pump running, thermostat on high, fan engages, after a few seconds, you can hear the igniter sparking. NO THUNK from a gas valve opening. Igniter continues to fire several seconds and stops. Fan keeps running, no heat felt at exhaust. After awhile, the igniter fires again. Control board is continually supplied with 120v... I'll repeat, I am NOT losing 120v to the control board.
I am guessing the control board is not supplying 120v to the gas valve (control board bad) or gas valve bad. I have NOT been able to measure anything over a volt or two on the purple line, so my next step is to apply 120v to the gas valve. Don't worry, I'll shut off the gas at the heater and even in the basement at the home's manifold. I know what I'm doing.
I do wish I understood the gas valvue unit itself better. It gets neutral, the purple line already mentione, but then has some type of jumper block. Can anyone describe in lower detail how the gas valve ITSELF isworking? Example, If I knew that the gas valve is "dumb" i.e., it either gets 120v or it doesn't; it either opens or it doesn't, then if I have to troubleshoot the control board, I know that it is "only" switching 120v on or off. What I cannot figure out, is whether there is any feedback signal back to the control board (not unless it uses that same purple line/feedback is incorrect voltage drop).
Does anyone know these things well enough to speculate?