I dont know how many, if any of you guys work on this type of stuff
but I thought I'd share my recent experience with this boiler.
Last week I went out on a call to a job site that I havent been to
before. The complaint was a noisey boiler. It a fin tube type. At
first it sounded like a flow problem, howling sound in the HX. I
checked the flow, delta T going through the hx, and so forth. Every
thing was ok. I then opened it up to inspect the burners and HX. If
anyone has ever worked on this boiler you know its not an easy task
but what I found was several cracked burners and a sooted HX. I
replaced the bad burners and cleaned the hx. Reassemble and it ran
sweet as pie.
Now on to the reason for this post. After I did the repairs the owner
wanted the CSD-1 preformed on both boilers which I did.
When it got to checking the flame safe guard I clipped the wire going
to the flame sensor and all three stages kept burning. At first blush
I though it was a faulty Fenwal ignition mod. so I switched them from
one boiler to the next. The boiler I removed it from had passes the
test with flying colors. Switching the module had no effect and the
flame kept burning and in fact the boiler lit without the flame sensor
in the circuit. Not good. Not good at all. I disabled the boiler
and told them I'd be back
Well a week went by and today I was able to get back to it, ive been
real busy which is a good thing. After checking the internal wiring
and wiring to the stageing controls Ive narrowed it down to two
things. All wiring is good. As you all know any system that uses
rectification be it through the HSI or flame rod, the GV's should shut
down if no flame is sensed. The module should drop out. This didnt
happen and could be a serious problem. Imagine a bad HSI, a call for
heat and gas dumping in. Something eventually will lite it off and it
wont be pretty.
In the end run I swapped out the main circuit board which has eight
relays on it. The problem traveled to the known good boiler so its
either in the circuit board or a relay. Tomorrow I'll figure out
which and all will be good again. Im enclosing a ladder diagram which
I know is a no no but oh well it beats flaming dickheads. Take a look
and see if you can determine the problem from the ladder diagram if
your interested. If not, carry on.
From my point of view I think this is a serious design issue.
Points to consider
1. closing of gv1 which is in the burner section that has the flame
rod still allows gv 2 and 3 to open.
2. disconnecting the flame sensor still allowed it to fire and run.
3. closing off gv 2 and 3 and disconnecting the flame sensor allowed
gv 1 to open and run. Eventually blower 1 shut off and blower two
stayed on and the gv1 stayed open producing a nasty yellow flame until
I shut it down.
Looking at the ladder I still dont see how this is possible but thats
what happened. I think its either a stuck relay or something is
bridged on the board. Both boards visually looked fine.