FuelMizer SR501-OR-4 Switching Relay with Outdoor Reset

I chose this Outdoor Reset over the Tekmar 256 because it's a little easier to install on my particular boiler and doesn't require an external transformer like the Tekmar 256 does in my situation. The Fuelmizer doesn't have the fancy LCD control panel and display but I knew once I had it set up I wasn't apt to ever look at it again. The fancy display would have been wasted on me. I've only had the Fuelmizer installed for a few weeks but so far so good. It does exactly what it's supposed to do. The only snag I ran into which was my fault was I didn't turn the low setting down on the boiler aquastat lower than the 140 degree low setting on the Fuelmizer when I first installed it. Until I figured out what was going on the burner was starting and stopping independent of the Fuelmizer. In other words the red "Boiler" LED on the Fuelmizer wasn't coming on when the burner was running. I turned the aquastat low setting down to 120 and now the Fuelmizer has complete control over the burner. The "Boiler" red LED is supposed to come on whenever the burner is in operation. At first my LED wasn't coming on when the burner was running. Now it works the way it's supposed to.

Great for handling anything that's not a design day with an oversized boiler and oversized radiators typical of older houses. Went from overshooting thermostat with 190 degree water through the baseboard to nice long cycles of moderately hot water. Huge improvement in comfort and less heat (and money) up the flue. Based on past experience and per Siegenthaler you'll probably save a good 10% on gas/oil if your aquastat high-limit is currently in the 180-190 degree range. Also looked at the competitor's fancy outdoor reset controller but would have needed a separate 24v transformer so I went with the less expensive Taco and couldn't be happier. Saw another reviewer couldn't get his supply sensor to read temps accurately; I had the same 10-15 degree variance when I strapped the supply sensor straight to the pipe. The solution: thermal paste/compound. Easy to find reviews for the stuff as it's used when installing heat-sensitive computer parts. Cheap too! Just put a little on the flat part of the sensor, wrap your finger in plastic wrap, then use your finger to spread a thin layer over the flat part of the sensor. Strap it to a clean supply pipe and you're good to go! With DIP switches #1 and #2 on for a 140 degree minimum supply and a 20 degree differential and outdoor temps around 40 the temps were bang on: my infrared thermometer gave me 129.5 when the boiler fired on and 150.5 when it clicked off. Close enough to the 130/150 you'd expect for $5 and a minute of your time, highly recommended if you're putting in the effort to retrofit your boiler.

For years the only outdoor reset device available from the Taco family was the PC700 unit but if you didn't have an -EXP series SR controller you couldn't use the PC700's plug and play adaptor and were out of luck, and everything else from other sources was mostly a work around, originally built for other purposes. So when they came out with the fuelmizer I was very interested. I have a late model Crown non-condensing boiler with indirect DHW and so the DIP switch 1 setting on the Fuelmizer to let the boiler go no lower than 140deg is important (don't forget this if you have the same situation). If you have some background in electro-mechanical protocol, installation is a breeze, and the clear labeling on the board makes it feasible even for a novice. Note you must specifically locate and insulate the boiler sensor, and when I followed the directions, the boiler restarted at 140degrees indicated by the boiler's thermometer (if there was a thermostat call). Here is a representative start up scenario. I had the breaker for the boiler shut off during installation, and enough time had elapsed so that when I repowered, all 4 indicator lights went on. The power light. There was a DHW call, so that light was on, and since that is a zone on the controller there was also a "thermostat" light and since a DHW call overrides the outdoor reset the fuelmizer drives the boiler to high limit, the boiler light went on. After the DHW was satisfied, the DHW light went out, and since the outdoor reset was back in charge, the boiler light went off soon after. The thermostat upstairs was cranked up so the thermostat light was on, the circulator pump for it was pumping, but the boiler was off. Eureka!! It took about a half hour to bleed the boiler temp down to 140, and the boiler started again to about 158 (the outdoor reset point on a 45deg day). Yes, it I had a condensing boiler this config would be more efficient, but in this config I figure I'm saving 10-15% in fuel costs.

Hello: I installed the Fuelmiser on a Weil-Mclain Model gv5 140,000 btu gas fired boiler with three zone valves and one circulator Pump. The stock boiler had a temperature differential of 20 degees at the boilers gauge which is measuring at the water. The fuelmizer has two settings 20 degree and a 10 degree Differential. The best I could get on the 10 degree differential setting is 25 degrees at the boilers gauge I have the sensor straped on to copper pipe and I moved to different locations. I think the engineers didnt take in considertion the heat transfer thru the pipe.I think the senor would work best in a submersion well. The sensor work best wired with 14 gauge wire in conduit. (Read Tekmar sensor instructions). The best differential I got with 20 gauge bell wire was 30/35 degrees at the boiler gauge. The differential will slow your heat recovery.The unit is well made and easy to install and will save you aprox.14%. I plan on change the sensor to a submersion well. Pexsupply has great service they reply to Emails,shipfast. Taco Service??

You need to be comfortable with line voltage electrical work as this connects to the AC power and circulator pump as well as Low voltage thermostat. Note: The basic internal wiring is for 2/3W Heating Stats. I suggest that the Heating circuit of a Heating/Cooling system leads be extended TO this device. I was hoping for better fuel saving and less overshoot, on a really old, 1947 radient system. System lag due to a thick slab and heat losses makes recovery from a nighttime setback really slow. I would not reccommend this solution for this kind of system, payback will be out many years.

I just installed this device, and it has been performing exactly as described. TACO Tech support was very responsive when asked a question about the aquastat settings, I have no doubt this product will be saving me money in the upcoming year and paying for itself in no time.