Welcome to the DoItYourself Forums!

To post questions, help other DIYers and reduce advertising (like the one on your left), join our DIY community. It's free!

gas valve short cycling


jeweler's Avatar
Member

Join Date: Jan 2008
Posts: 97
CO

02-12-18, 01:13 PM   #1 (permalink)  
gas valve short cycling

Not sure the gas valve is the problem. While the boiler is heating the water the gas valve clicks, shuts off the gas, then in about 10-20 seconds re-energizes the hot wire ignition, re-lights the burner then repeats the shut down and re-start in about 2-3 minutes. This continues until the boiler gets up to the aqua stat upper limit of about 190 degrees. Of course this takes much longer to get up to temperature because of the interrupted heating cycle. Does this mean a bad gas valve or aqua stat or what?

The boiler is a Teledyne Laars JVH 100P induced draft (later changed to natural gas) installed in 1996. This is a high elevation derated unit for 5001-8000ft. The aqua stat (Honeywell L4006A1967) was replaced 2011, the gas valve (Laars V2001800) was replaced in 2006.

What do you suggest I do to verify which component is faulty? Any advice sincerely appreciated.

 
Sponsored Links
jeweler's Avatar
Member

Join Date: Jan 2008
Posts: 97
CO

02-12-18, 04:25 PM   #2 (permalink)  
Can no longer modify the original message so I am adding a few thoughts.

I am now wondering if it might be the pressure switch that verifies the fan (inducer) is working. I have verified the fan is good but am wondering about the pressure switch. If the switch is going bad and does not see constant pressure it could switch off the gas valve. If this pressure switch was going out this might be causing the problem. Is this reasonable? How do I check this?

Similarly, there is a flow switch that verifies the Taco circulation pump is working. Could it be the flow switch?

I am adding more questions or possibilities and am looking for advice as to what is most likely. Prefer to not throw parts at this. I can short or bypass these switches to see but am reluctant for the obvious reasons. Don't want to take chance that something goes wrong while these switches are temporarily taken out of the circuit.

Any suggestions from those who have the experience?

Thanks


Last edited by jeweler; 02-12-18 at 04:30 PM. Reason: clarify
 
PJmax's Avatar
Group Moderator

Join Date: Oct 2012
Posts: 41,205
NJ

02-12-18, 07:22 PM   #3 (permalink)  
Since the ignition system was changed from original manufacturer.... the factory wiring diagram won't be of much help. What is that using for an ignition module ? Post the model number.

Most ignition modules run on 24vac and it comes thru the limit loop and possibly the pressure switch.
You can monitor the 24vac at the ignition module..... if that is going out and causing the burner to shut down.... you need to follow that line back and see what it passes thru.

If the 24vac to the module stays constant and the burner is shutting down.... there is a burner monitoring issue... possibly a flame sensor issue.

Gas valves don't short cycle.... their controls do.


~ Pete ~

 
jeweler's Avatar
Member

Join Date: Jan 2008
Posts: 97
CO

02-13-18, 09:07 AM   #4 (permalink)  
I was not clear. The ignition module is unchanged from the original. The boiler was originally set up for propane and changed to natural gas after about 2 years. Otherwise everything is as it came from the manufacturer.

Is it safe to temporarily bypass the pressure switch? This is the one that verifies the induced air blower for the exhaust is functioning. I figure this is the simplest to verify first. There is a approx. 1/4" hose going from the blower to a diaphragm that opens/closes a switch. If I unplug one of the wires the gas valve shuts down immediately. I am guessing this switch may be going out.

 
roughneck77's Avatar
Member

Join Date: Oct 2016
Posts: 485

02-13-18, 11:37 AM   #5 (permalink)  
No, do not jump anything out.
Use your meter to verify which component is opening.
If it is the pressure switch, verify correct draft with a manometer.

 
PJmax's Avatar
Group Moderator

Join Date: Oct 2012
Posts: 41,205
NJ

02-14-18, 11:24 AM   #6 (permalink)  
If I unplug one of the wires the gas valve shuts down immediately. I am guessing this switch may be going out.
No.... that is exactly what should be happening. If you read what I wrote...anything open in the safety loop will not allow the boiler to fire.

Since you are trying to troubleshoot something electrical..... you should have a meter. Even a basic $15 analog meter from the home improvement stores will work. You set the meter to AC volts and connect the leads directly to the sensor you are testing. The probes can usually be inserted carefully into the plastic connectors while they are connected to the switch.

If the sensor/switch is normal.... you will not read any voltage.
When it fails or opens.... you will measure 24vac.

With the pressure switch. With no call for heat you will measure 24vac across the switch leads. When the inducer starts and gets up to full speed.... you should measure 0v and it should stay that way all the way thru the cycle. If you see any voltage.... the switch is opening.


~ Pete ~

 
Search this Thread