boiler ignition problem


I am having an intermittent problem with the boiler for my hot water heating system. The boiler is a Peerless, uses natural gas. The ignitor control is a White-Rodgers 50E47-150. What happens is I notice the house is kind of cold, see that the temperature is well below what the thermostat is set to, and go down to look. The circulating pump is running but the boiler is cold. The red light is flashing on the ignition control module. According to the troubleshooting guide for the control unit, this indicates the fault is likely outside the module itself. However, turning off power to the system and turning it back on again makes it restart and then it works fine for a while (like a couple days). When the system fails, I don't know whether it is because of a failed start or it is shutting down prematurely while running, although it always starts OK after the power off/on.
I am thinking that the ignitor must be OK since it works whenever I am watching, and it would either work or not work at all. Perhaps the flame sensor is not consistent? Problem with the gas valve? Any suggestions welcome as to things to test or guesses as to what the problem most likely is. Thanks, -- H
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Heathcliff wrote:

I would clean the flame probe first. Very fine steel wool or the like. Dust any particles off afterward.
Less likely is an intermittent board itself.
Jim
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Speedy Jim wrote:

Here is an update. As usual Speedy was spot on. I finally was able to observe the boiler failing when the off/on procedure stopped working. The ignitor would go on, flame would go on, but then shut off after a couple seconds. That confirmed for me that the flame sensor was not working. I tried cleaning it off with steel wool but to no effect. Then I took it in to my local HVAC parts store (in a mild panic as the house got cold) where they told me (a) they have no replacement for it in stock, and even finding out where to get one might take a couple days, and (b) it tested OK for continuity, I just need to do a lot more cleaning. So I took it home and spent about 15 minutes really going at it with the steel wool. After that it worked. Didn't realize how much elbow grease was required.
Side note: as I was returning from the parts store, when I got out of the car dang if the darn thing didn't catch on something and the wire pulled out from the sensor. Some bad words were spoken. I cleaned off the end of the wire and managed to jam it back in, good enough for it to work, this is the second day with no problems yet (fingers crossed).
Further question: I would still like to have a spare on hand for this, but apparently this model is discontinued from the manufacturer (White-Rodgers) and they have no suggestion as to a substitute. Does anyone know how interchangeable these flame sensors are? It is your basic metal rod, about three inches long and maybe 3/32 in. thick, emerging from a ceramic body, with a wire coming out the other end. I noticed an ad on Ebay for a similar-looking model, the ad claims it can be trimmed and bent to suit. That makes it sound like they are not so precisely spec'ed. -- H
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Heathcliff wrote:

Without observing a failure and/or serious diagnostic tools, you'll just keep chasing it. Cheap easy-to-replace stuff comes first to mind, as does checking the circuit board for bad solder joints.
Another item to check is the size of the pilot flame, and the little holes (jets) that go from the pilot to the burner proper. Sometimes the pilot flame is a skosh too small and it won't reach the main gas jets, and sometimes the gas jets that go between the pilot/ignitor and the main burner plug/corrode.
I believe even in a 'pilotless' system, the ignitor lights a small gas jet, then that gas jet lights off the burner proper.
Be aware that messing with it, you may booger something up that could cause a hazard, or require a service call/parts replacement. If there were to be a fire, your homeowners insurance could be affected if it was caused by the furnace after you worked on it.
Dave
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I'm wondering if the problem is something else entirely, like air in the system. I realise that sounds odd, but I saw a system fail just like this recently- and though I didn't get a chance to talk to plumber who set it straight, I did see he had installed air purge valve.
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