Short cycles on boiler

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Old 03-26-11, 05:19 PM
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Short cycles on boiler

Hi all, hoping someone out there can help me.

We have been living on our house for about a year now, and had been having problems with our pilot light staying lit. After replacing the thermocouple, then the gas valve, and then having the gas company replace the regulator and meter - twice, we still were having problems. The service company we were using were stumped, but they recommended installing an automatic pilot re-lighter. Seems to work ok, but when the thermostat calls for hot water, or the domestic hot water the boiler cycles on and off in very short cycles about 5 seconds. Keeps doing this - you can hear the pilot light ignition click and light then the burners burn for about 5 seconds, then shut off, and the pilot ignition starts clicking again. So today I replaced the thermostat thinking it could be that, but still having the same issue. The house seems to stay heated, and we have hot water, but I'm thinking it can't be good for the pilot igniter or valve to cycle so much.

The boiler is a LAARS Mini-therm II model JVT160NDII. Any help or advice is greatly appreciated.

Thanks,
 
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Old 03-26-11, 06:29 PM
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Hi.

The service company we were using were stumped, but they recommended installing an automatic pilot re-lighter.
It does not make sense that they put a auto pilot igniter on. The issue should be found. Did you have to pay for that? I probably would not have paid for anything(parts) since they did not fix your issue.

First of all is the pilot still going out? I guess you would not know and it seems like its by-passing a saftey feature. The JVT is a standing pilot. If the pilot goes out and its not the t couple the somethings wrong.

You are CO. There are air shutter adjustments that need to be made if high alt. Might cause pilot issue.

There blocked vent switch would cause the pilot out, but it would need to be reset manually.

The roll out switch would cause this pilot out issue, but also would need to be reset.

Inlet gas pressure too low or Inlet gas pressure too high causing an unstable blowing pilot. Inlet gas pressure to boiler should be 5.5" to 10.5" water column on natural gas. Did they verify even though they changed everything?

Plugged or undersized pilot orifice

Dirty pilot/damaged pilot or bad t coupler.

Do you have a low water cut off? These somtimes go off sporatically from dirt/age etc.. and may cause pilot outage.


What does the pressure and temp say on the boiler gauge???

Here is the manual.
http://www.laars.com/LinkClick.aspx?...=1607&mid=4009

As far as short cycling did it do this befor they added the auto pilot device?

And from your post you have a indirect HWH? Zone Valves?


Mike NJ
 
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Old 03-27-11, 07:29 PM
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Thanks for the reply. I'll try to clarify the situation. The pilot is not necessary in the new system, it only lights when the burners turn on. The unit they installed is a Honeywell S8610U Continuous Retry.
The repair company looked at the gas pressure coming into the unit and said it was within spec (I think it was around 6 in WC with a slight drop when the burners fired.) The repairman from the gas company assured me that I was getting good pressure and flow from the regulator after he replaced it.
It seems like the issue is related to wiring or one of the electrical components. When the thermostat or hot water heater calls for the burner, the ignitor lights it just fine, it runs for about 5 seconds, then shuts off, only to restart immediately until the water is at the correct temp.

The boiler water tamp and pressure are 180 F and 15psi once it stops short cycling.

As for whether the unit did this before, I don't think so, but then again the pilot light wouldn't stay lit. Maybe this was the problem all along. It only short cycled once while the repairman was here, and he said I might replace my thermostat, which I did. Of course it short cycles every time now.

At any rate I think you have me convinced to have them come back and fix, or if they can't find a new service company. Even though this is a DIY forum, this may be beyond my abilities (or at least beyond my time to dedicate to figuring it out!) Any other advice or suggestions? Thanks again.
 
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Old 03-27-11, 07:41 PM
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Yes well the JVT is a standing pilot and you are saying they converted your system to a JVS??????????

Not acceptable to me.. Thats me.

Good luck.

Mike NJ
 
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Old 03-27-11, 07:56 PM
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The Honeywell S86 is not a re-igniter for a standing pilot but an intermittent pilot assembly. It would have required a different combination gas valve from what the system had when the standing (constantly burning) pilot was in service.

What you are describing is a lack of "main flame proving" and THAT is shutting down the main gas valve and causing a retry of ignition. There should be a rod (about 1/8 inch diameter) mounted on the side of the burner(s) farthest from the pilot and located so it is enveloped by the flame of that burner. It will have a single wire that goes back to the control for the ignition and gas valve. You need to clean that rod (called a flame rod) with a Scotchbrite pad to remove oxides deposited by the flame. Do this even if you cannot see any kind of coating or anything on the rod. Make sure the wire connections are clean and tight. If this doesn't work post back.
 
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Old 03-27-11, 08:35 PM
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And especially check that all of the GROUND WIRES are in place, and all the connections are clean and tight. Those flame rods work off MICROamps of current flow. If you've got a bad ground, it won't work.
 
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