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Tim H.
Tim H., HVAC Professional
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My Honeywell aquastat relay L8148E is not working. Why?

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I have a Honeywell Aquastat Relay L8148E. When I turn the thermostat to call for heat nothing happens. If I lift the Switching Relay (close the circuit), it works. When I let go, the circuit opens and the furnace stops. I stuck something under the Switch Relay to keep the circuit close. It is 10 degrees outside. What should I do?

Thanks for giving me the opportunity to help!

Put a jumper wire across the T-T terminals inside the unit (turn power off first) and let me know what happens. Does the unit work with jumper in place?

Customer: replied 5 years ago.

On page 4 of this PDF, figure 3 looks similar to what I have except my Switching Relay is turned 90 degrees so that the word Honeywell is horizontal. The same little piece of metal with with Honeywell on it is the piece I lift to make it work. It seem to work correctly when I have something stuck underneath the metal piece.

As far as putting a jumper wire across the T-T terminal, can you tell me which are the T-T terminals according to the figure 3. I see something labelled TV and another labelled T.

Put a jumper across T and TV. Currently your thermostat wires are across there. I'm just trying to eliminate the thermostat as a source of the problem.

Customer: replied 5 years ago.
Yes the jumper worked.
Then you need to replace your thermostat.
Customer: replied 5 years ago.

I did go around and check my thermostats and found one of them looks like someone bumped it. I could not turn the dial, it was kind of pushed in. I took off the ring straightened it out and it looks like it works normal.

Are they difficult to change out? Do I just take it off the wall and put a new one there? Do I have to turn off electricity before doing it.

Best to turn boiler power off first. They are not difficult to replace. You will want a heat only thermostat. Keep track of which terminals the wires go on to make new one easier to install.

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Customer: replied 5 years ago.


I changed the thermostat, but still doesn't work. I talked to the Honeywell technician on the phone and he had me take the thermostat off, test the voltage in the wires (24v), and twist the wires together. He told me to turn on the furnace and see if it works. It didn't. He said that it is not the thermostat then.

It did make me think, even if one of the thermostats wasn't working, shouldn't the furnace run if one of the the other 3 thermostats were calling for heat? Where do I go from here?

You said you jumped T and TV and boiler started, correct? Most systems are set up where if any of the end switches are made from any of the zone motors, it will close the contacts at T and TV. Check your wiring from all your end switches from your zones. They should all be tied together and go to T and TV. These wires will be red.

Customer: replied 5 years ago.

Yes, the boiler starts right up if I jump T to TV. I have 4 thermostats. Each one has 24 to 26.9 volts. Since there is power, wouldn't that mean they are all connected? I traced the read wire from the Aquastat Relay through all of the zone valves (4 of them) until it disappears up through the floor. I assume that it is going up to the thermostats. I can't follow it.

The reds from the end switches (if you have Honeywell zone valves) all tie together and go to the T and TV on most boilers. This forum is not meant to go into a complete description of how a boiler and zone system works. But basically your thermostats provide power to the zone motors which slowly open and make an end switch. The end switch then "jumps" T and TV at your boiler control starting the boiler.