weil mclane boiler inition issue

mburg

I just looked at a weil mclane boiler that wasn't igniting the pilot. when I got there the igniter was energized and clicking and gas was going to the pilot but it wasn't igniting, I shut the power and when I turned it back on the pilot ignited, but even after the pilot was lit you could still here the igniter, does that igniter run constantly? Also I figure I should change the ignition box and igniter, any thoughts? this is the wiring schematic

Abracadabra

Ignition module

Robert O'Connor_12

Does it look like this?

mburg

That's exactly what it looks like Robert

unclejohn

I think the igniter is always powered and the pilot flame was supposed to ground it out. But if you have a mercury flame sensor, do every body a favor and replace the valve, pilot and igniter. That thing is at least 25 years old which is a long time to depend on a gas valve.

mburg

Replacing everything isn't a option for this guy, if it's supposed to shut off and isn't, changing the ignition module and pilot assembly should take care of this correct? I'm not familiar with the mercury flame sensor it's all a little before my time

JUGHNE

The mercury flame sensor cap tube is quite fragile, especially at the gas valve and if broken is done for.
I had that situation and the best option was a change back to a standing pilot valve with the thermocouple fitting quite well where the mercury sensor was.

That relight module uses flame rectification, if so the ground connection between the module mounting screws and the pilot hood or sensing bulb is baked out then there would be intermittent problems. Just loosen and retighten the screws on the module to cut a new path for ground for that end of the circuit.
If the hood or sensor is corroded a little cleaning might complete the other end of the ground path. The pilot flame must impinge on the hood and sensor.

unclejohn

Incorrect because your not going to get that pilot assembly any more. Things don't last forever, lets say the boiler is 30 years old which is probable. We don't discuses price but lets just say if he replaces the parts he will probably get another 10 years trouble free. So divide the cost by 10 and sell it that way.

JUGHNE

One of these I dealt with (was installed in 1982) had a broken mercury cap tube. The supply house sent a standing pilot gas valve as being "cross referenced" replacement. The pilot burner was reused and T-couple fit where the mercury sensor was.
The customer was an 80 year old widow who didn't worry about the gas usage of the pilot.
Mburg's problem could be bad grounding, I would try that first.
I believe the mercury cycling sensor system had a short history in gas controls before something better came along.

mburg

Assuming it's just a grounding issue, there is nothing that points to the mercury sensor as being bad when the pilot is lit it does fire the main burner, so I'm gonna start with the grounding issue

JUGHNE

Please let us know...Thanks.

Tim McElwain

You have a White Rodgers Cycle pilot system. The ignition module is simply a pilot relight device. It does not use microamps or flame rectification. The flame simply shorts the high voltage spark signal to ground through the flame, the principle is called " flame conductivity".

The first thing to do is clean the pilot as the mercury bulb needs a very hot flame to boil the mercury. When the mercury boils it will trip a SPDT switch that is plugged into the gas valve that will power the main valve and the pilot will light the main burner gas. The tip of the mercury bulb should glow "cherry red" .

If after cleaning the pilot the mercury switch could be the problem. Simple test pull the mercury sensor and hold the tip in a flame and check with an ohm meter (continuity) to see if the switch walks over.

What is the number on the mercury sensor? It can be replaced by 3049-64 you may have to shop around to find one Perhaps E-bay etc.

There is also a replacement gas valve in the 36C84 or 36C94 Series. In particular the 36C84-912.

If none of this works then you will have to do a retrofit which will include replacing the pilot assembly itself as the mercury pilot will not accept the spark igniter/flame sensor. A Honeywell Q345 pilot would probably do it for you or a Q314 used with a Y8610U Honeywell retrofit kit.

Last of all try shopping around for a White Rodgers Cycle Pilot replacement system.

Could be time for a new boiler???

JUGHNE

The reference I'm using is the Rheem training manual for Spark Ignition Systems using White-Rogers Controls. Yes, this is for forced air furnaces but they both appear to use the WR 5059-122 with the 36C94-213 gas valve.
They use the term of flame rectification and flame conductivity interchangeably in their book, it just appears to be an issue of semantics. In any event I assume the return ground path must be of low resistance for proper pilot lighting.
There is also a pressure switch in the gas valve which used to give problems if gas pressure dropped below 2" WC. There was a "fix it" resistor kit available for the NG valve.

I thought the Y8610U 4001 would be a good repair for my situation. However the new pilot would not mount in the correct position and delayed ignition would occur. So that retrofit kit is back on my shelf. Perhaps the boiler pilot burner mounting would be more user friendly than the Rheem furnace was.

I just mention the retro kit as I now have one with minor wrench marks on it and can not be returned, they are not cheap.

FWIW: I would be reluctant to even pull off the valve end of the mercury sensor, seeing how easy the cap tube snaps off after maybe 30 years.

Tim McElwain

What does Rheem say you should get for microamps and how do they instruct on taking them with a mercury sense system?

I have replaced several White Rodgers Cycle Pilot Systems with the Y8610U using in two instances the Honeywell Q345 pilot and in five others the Q314 which is a thermocouple/powerpile adaptable pilot sort of the workhorse of the industry, The hardware from Honeywell fits nicely into that pilot in fact every class I do using the Honeywell suitcase trainer that is the hookup I demonstrate.

The ignition issue can be solved by using the correct hood position on that pilot either left - right or straight. I do a pilot safety turndown test on every one of those and they work fine. By the way two of those retrofits were on Rheem furnaces. The Rheem furnaces however need the low profile adapter for the pilot.