ghost firing burner

bruce_21

My client's Beckett burner will regularly but seemingly randomly fire for about 10 seconds then shut off. There are 4 zones: indirect HW tank and 3 air handlers going thru a Taco SR504 EXP (no cards installed) to the Honeywell L7224/L7248 aqua-stat.



I've been in the basement doing other work and witnessed this phenomenon, but its over before I can even get over there to look at the Taco's little lights or anything.



What to look for, check?

icesailor

Ghost Firing:

Well, if it were old, I'd tell you what it is.

But this may help anyway.

It probably has to do with the thermostats and zone valves if they are Taco 57* type wax motor valves. If you have non-electronic thermostats like Heneywell T87's, the heat anticipators MUST be set to .09 amps. I set them to 1.0 or as high as I can set them. If they are El Cheapo builders models that can not be set for over .08 amps, change the thermostats. As the temperature drops, the thermostat "anticipates" when to turn on. Without this critical adjustment, the valve starts to open, the heat anticipater sends a slug of current into the valve and the valve starts to open. The #2 and #3 contact are made and the burner starts. At the same time, the thermostat has already shut down. It could also be a polarity issue. If it is a gas boiler with transformers, you may need isolation relays because of "ghost currents". If air handlers, you definately need isolation relays.

If they are digital electronic thermostats, you may need isolation relays or a proper setting on the cycling adjustment.

When this "10 second" start happens, does it again start a few minutes later and run for over two minutes and then shut down? If it does, than what I have described is probably what is happening.

bruce_21

there are no

zone valves. There are 4 separate pumps controlled by the Taco SR504 which on a call for heat from a zone closes its "xx" terminals which are connected to the L7224's "TT" terminal. I don't think there is an anticipator setting possible on the SR 504 pump relay. There are fancy electronic stats controlling the three air handlers, but doesn't the SR504 serve as an isolation relay?

meplumber

Sounds like the end switch in the SR is going bad.

I have seen this before Bruce with both the SR's and the ZVC's.  (And Argo's too).  The end switch (x-x) will flutter for a while before dropping out completely.



I am not sure if Mr. John Hazen White has read this post or not, but I am sure that he could tell us some of the causes of premature end switch failure.  I remember being told once that it had to do with irregular current or voltage coming in from the house to the SR or ZVC.  It causes the contacts to weaken over time.  (Or something like that.)



I would start my search for a cause there.



Good Luck.