Can you smell gas after the "click"? If so, you have an ignitor problem or one or more plugged burners. If not, has the gas recently been off? You may have air in the line.

Actually, The gas has been of for couple month, and i didn't smell gas. only the first time when i opened the gas valve, and after that i didn't smell gas. What shout I do. Thanks for your help

Hi Repair guy

What should I do if air in the line. Can I light the heaer by hand. Thank for your advice

Let's assume there is air in the line if the gas was off for any period of time.

The heater will lock out after three tries to ignite. Each time it tries to ignite, after that click, you will usually hear the gas flowing at the meter. It will flow for 7 seconds and then shut down and retry for a total of 3x. If the gas has not made its way through the pipe in those 3 tries, you will need to turn the power off to the heater and do it again. In most cases, it's about 5 attempts before the average gas line purges the air.

The giveaway here is if it is trying to ignite and you don't smell gas blowing out, you have air. The presence of gas with a good igniter will light as long as you have a good igniter and clear burners.

The quicker way to bleed the line is to open up the union in the line until you smell gas. Shut it off and then tighten the union.

Thanks for you reply.Where is the union locate? I 'm new to the sys, if you don't mind

Don't break the union, Instead reset (power cycle) the heater and let it cycle. If it times out again, reset it again. If the problem is air in the line, it will work its way out, and this method is much safer.

If you can't identify it, go with my suggestion and the same from Racket. You don't need to be getting into things you have no knowledge of.

Hi

After done all your sugesstion, I finally smell gas, but the service light still on. One thing I noticed that inside the burner, I can see the orange flame but it last for a second and then off after 3 cycle the it went to lock out mode. One thing in the back of the panel, other 3 led light 2 green light on the other (I belive PW or NW) green light on and then off as the servive light red on.
Any sugesstion or advice please
Thanks

If you smell gas and let it cycle several times AND cleared the lockout after it fails those 3x, you need to check the burner orifices for plugs and then the igniter. Checking the igniter means ohming it out or checking for continuity first.