AQ475

jacobsond

Wireing up a honneywell AQ475 outdoor reset on a hot water heat system.Multiple loops but only one zone and a chronotherm thermostat.No domestic hot water. The wiring is pretty straight forward for the sensors thermostat and circulator.. The terminals that say boiler aquastat is my question. Where on  the boiler aquastat do they hook up?

I hooked it up to the thermostat terminals on the original aquastat and the boiler works but the AQ475 dosent seem to control the reset temp. The original boiler aquastat is still in control of the boiler temp.

Steamhead

The Boiler Aquastat terminals on the AQ475

are wired to TT on the boiler. It is this pair of terminals that turns the boiler's burner on and off. 

jacobsond

checking the AQ475

Thanks for the reply. That is what I thought and the way it is hooked up.The aq475 has been hooked up for a few years actually but I never thought it was working correctly.Im learning on the wall here and just double checking. Today the low temp was -19F and currently at 1pm central it is still -13F. Now is a good time to check the high settings and I am getting conflicting results. I had the aquastat set at 160 the temp gauge on the furnace was peaking at 180 the reset high was at 180 and the low was 140.With these outdoor temps my Crown CXE-5 LP (150,000) was barely able to maintain 67 in my 2000sf home. So I have a discrepancy in my boiler temp. Is the aquastat correct or the gauge? Well 150,000 btu should be more than enough for this house. I turned the aquastat up to 180. Now the temp gauge is running over 190.The house is easly maintaining 68. Now to the setback control. The boiler temp sensor is not in a well it is just tied to the output pipe and insulated. I used an infared temp gun to check the temp of the pipes. Follow me on this. With the outdoor reset set at 180 the aquastat at 180 and the temp gauge reading above 190 the infrared measured about 170-175 on the outlet. I had to adjust the outdoor reset for a max temp of 170 and turned the min temp to off to get the outdoor reset to work. My temp settings seem to be all over the board. I would guess the infrared may not be accurate because of measuring the pipe is tough. The sensor on the setback may not be accurate because its not in a well. I am going to assume the temp gauge on the furnace is incorrect and going with the temp on the aquastat. I have confirmed the setback is working with my current settings. The setback is shutting the boiler down before the boiler aquastat would shut it down. If it ever gets up to +20 around here what would be a guess on the boiler temp if the outdoor reset is working?

Tim McElwain

With the outdoor

temps you are mentioning it brings to question the design temps of this system. Sub zero temps are the worst scenario for equipment operation. It also is related to whether a heat loss was done at some time on this dwelling. Controls can only do so much but are simply reactive to temperatures and other factors. I would look at several things including insuring you are firing at the maximum design firing rate of the boiler (a combustion analysis will show this) and also the flow patterns of the system as far as circulation. Start with those and work from there.