Boiler still runs even when thermostat is off

Dave_Dude

I have an ancient Arco boiler from the 1920's that runs my gravity fed heating system.  When I lit the pilot light this week, the burners kicked in even with the thermostat off.  I've disconnected the thermostat altogether and the burners are still going full bore.  If I disconnect either of the 2 wires to the gas control valve the burners die.   There is a box on the wall that says "Pilotelectorelay" R-105-I, and a temperature gauge connected to the boiler that says "Minneapolis Relay control model # 6510".   It seems like there is a short somewhere or a malfunctioning part.   Any advice on what order and what to check would be greatly appreciated.



Thanks!

Dave



ps. Is there a max temperature the system can reach before I should worry.

STEVEusaPA

seems like

your relay is bad.  Time to get some professional help in there.  And hurry before it gets cold.

Dave_Dude

Thanks Steve

Thanks for the quick reply.  Is there no way for me to troubleshoot/replace the relay?  Also, is this a standard part for any HVAC system or would a boiler expert be needed.  I ask because there are probably aren't a heck of a lot of boilers in the part of California where I live.  I might be on my own to fix this...

bill_105

Before the relay

What happens if you disconnect the wires before the relay? If nothing changes -relay time, as mentioned earlier.

Just curios - where in CA are you?

nicholas bonham-carter

arco problems

one thing you want to be sure of is the function of that control to keep the gas valve from opening if the pilot is out.

the aquastat should keep the water temperature from going high enough to boil the water. i am sure there is a reasonably accurate temperature/altitude gauge so you can see how well the aquastat is doing.

any experienced hvac tech should be able to find a new control, or you can get part nos off the old unit and ask here about the recommended replacement.--nbc

Dave_Dude

Finally traced everything

I appreciate everyone's responses.  I finally got time to trace how the circuit runs and found some surprising results.



1. The relay has been bypassed long ago.  As far as I can tell, the only controls in the circuit are the thermostat, the aquastat and the gas valve.



2. No matter what I disconnect, I still get voltage to the gas valve.  I've disconnected the thermostat and all the wires on both sides of the aquastat and I still have voltage at the valve. 



So now I have some questions:



1. Is it dangerous not to have a relay?  My system is gravity fed and doesn't have any pumps.



2. Is it normal to have any voltage at the gas valve if  the wires to both the thermostat and aquastat have been disconnected?



3. If the answer to #2 is no, sure seems like I have a short?



Thanks for your responses.



@bill -- I'm in Stockton.

bill_105

Come to think of it

I guess a gas valve setup 90 years old would probably have called it quits. I bet you only have in this order, 24V from transformer to thermostat to aquastat to gas valve then back to transformer, and maybe some wiring that got whacked. Whew, highly technical for me!

Now for Stockton and UOP. So I'm going to a Pvt. high school on the Feather River which was owned by UOP. Well the senior class (all 10 of us) gets to take a trip to Stockton and check out a college. Once left alone by our teachers we found out about the dorms. This was Animal House on the west coast! Those were the days!

Gotta be getting a little cool down there about now, It's 0 degrees here in Anchorage.

Good luck

Dave_Dude

Wow, Feather River Prep????

Bill,



 I've been to Feather River Inn (or whatever it was called) numerous times.  I love that old place.   UOP used to run camps up there and I was a counselor there in the 80s.  You nailed the wiring setup that I have - or at least I think you did.  The wiring goes into conduits under the floor in the basement, so it's hard to say which wires actually go where, but I believe that is what's going on.  So, back to my question -- is this a short somewhere?  The 24 volts shouldn't be at the valve with everything disconnected, right?



Thanks!

Dave