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Work4living 11-28-2010 07:37 AM

Boiler Not firing. Please help
I have a more simplified "Old School" Boiler. No low water cut off. Just simple aquastat relay, Honeywell VS8137A Millivolt Gas valve, Honeywell Zonevalves VF8043E1036 I believe.

Of course while I was there yesterday I didn't have any of my tools. I did notice the thermostat calling for heat the zone valve is open. The relay is closed and the circulator is running. The pilot is lit, but the gas valve is not open. The boiler does not fire. There is a switch on the Aquastat relay "honeywell L8048B1099" that says Auto and Manual. If I move the switch to the manual position I can get the boiler to fire.

I am of course worried that this bypasses the safety of the high limit but am unsure. The cover has enough wear and tear that there is no diagram on it and I am unsure of the wiring route.. I am thinking of replacement of the Aquastat relay unless someone has other Ideas. I did try the honeywell website with no help.

Since in manual mode fires boiler I dont think the problem is the gas valve or the mv generator but instead the Aquastat relay.

I will be going back to the house today for some clean up and will try to diagnose with my volt meter. Just hoping for a second opinion or idea.


yuri 11-28-2010 07:50 AM

Post some pics of the burner and wiring from it (route) and that relay with the cover off. I have never seen that situation as it would be illegal with the gas code as it is illegal to have any device which can bypass a limit. May have a combo circuit inside it. The manual position would be to start a circ pump I would suspect. Moving it to manual may jiggle the wiring and you may have a loose connection on the limit control screws inside it. Take them off restrip them to bare copper and it may work. If the copper is brown lightly sand it with emory paper, you need bare copper and perfect connections with millivolt systems.

Work4living 11-28-2010 08:00 AM


Thanks for you response.
I will get some pics for you. I am sure that at the point of install some 50 or so years ago this was totally legal. I am unsure as to the cause of the manual setting of course. I was only able to get the model numbers off the controls, and of course they are obsolete. I am sure there is a cross reference for newer parts just have not had time to research. I dont know for sure if it bypasses the limit or not. I am hoping someone may have worked with one of these and would be able to offer what honeywell won't. Just like I am unwilling to pay $15.00 for advice from an online tech who will tell me I need to have an hvac tech come out. I would rather Pay a tech to come out. Of course i would also like to improve my trouble shooting skills and get some Boiler time in on my own equip. My skills are mainly in the Plumbing field, however I have a little experience in boilers too.

beenthere 11-28-2010 08:10 AM

Manual mode does NOT bypass the high limit. It only makes the boiler maintain temp without a call for heat.

Just because the zone valve is open. Doesn't mean the aquastat is receiving a call for heat. Let the boiler cool down. Remove the wires from the aquastat's TT terminals. Jumper them and see if the aquastat brings on the burner. If it does, then the aquastat is not the problem. And you need your meter to check what is not sending the 24 volts back to the aquastat TT terminals..

yuri 11-28-2010 08:11 AM

Have not seen one of those with a bypass in 32 yrs and I have seen thousands of old boilers. If it is a limit control it should have a adjustable setting of 180 F to 200F max. There are combo types with 4 screws/2 sets of contacts. 1 for limit and 1 for a circ pump. Circ pump usually set at 130-150 to cut in.

Work4living 11-28-2010 08:20 AM

Thanks Been!!

I appreciate it. I will take your suggestion and yuris too check My connections take some pics and also try to trace out my voltages. Do you have any diagram of the wiring routes by chance??


There is a limit control it has 2 screws the setting is from 180 to 200. It is set at 180ish. The unit sits on its side and there are other screw terminals in the lower right of the unit as it sets. To the best of my memory they were labeled circ., Millivolt, and line. Now of course this is from my memory and it was a bit late last night, I stopped by to check on things on my way back from Detroit.

I will get better info for the both of you. I am rest at ease a bit more. It sounds like I can leave it in manual mode for a short bit till I get this all figured out.

Work4living 11-28-2010 01:47 PM

Ok, Got it figured out.

There is a wire that runs from the contactor on the low voltage side that is pretty much fried. Insulation brittle as hell. Anyway the wire is disconnected and the reason for not being able to operate in auto mode. I was going to try and replace the wire but there is no way to reattach the wire to the contactor...Thus i will order a new aqustat relay.

beenthere 11-28-2010 01:49 PM

The coil of that contactor is probably shorted or shorting out. And is why that wire got hot and brittle.

Work4living 11-28-2010 01:55 PM

I swear what is the world coming to when a 50 year old control fails.....LOL

Thanks for the help!!! I am just glad to have found it. Hate it when you kinda know whats wrong but cant prove it...

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