Well, we’re deep into the heating season and listening to that boiler run and run is not going unnoticed. Every time it starts we feel our wallets getting a bit lighter and our blood pressure going up. On top of this things are pretty tough economically. Believe us, we notice it too! Let’s go over some things we can do to lighten the load at least.

Our remarks must be predicated by noting that the older your system, the more likely you are to benefit from this posting. Additionally refer to our other postings to gain insight to other improvement opportunities.

Please note the highlighted text links for referencing ease.

Firstly, if your system has any age to it, most likely the boiler is over-sized for your application. This happened two ways. Your boiler was over-sized when originally installed, the “standard procedure” until recently, or you have made energy improvements over time to make it become that way, or both. Listening to your boiler cycling rate on that deep cold January morning will confirm this situation.

Now we are assuming that your boiler has been THOROUGHLY CLEANED when serviced and properly tuned. If your serviceman shows up without heavy cleaning brushes and vacuum cleaner, trade him in!

Opinion varies on this, but if your unit is running less than 50% of the time on your deepest outside cold point(s) you are likely over-sized. So much for peak demand assessment and tuning. The aggregate of the more subtle energy-stealer items is likely more significant overall.

Applicable to your situation or not, the most common and most aggravating situation we find on older systems is incorrectly wired controls, particularly of circulators and the occasional zone valve. This winter again we have had several calls related to poor installation of controls and relays. (Refer to our blog ‘Plumbing Guys Plumb, Heating Guys Heat’ that vents our frustrations in this regard.) Additionally is having the wrong Master Aquastat for your system operating parameters.

The Master Aquastat is the primary control on your heating system and defines its sequencing, correctly or not. To determine if yours is correctly defined we must go down a checklist.

  1. Do you generate your Domestic Hot Water (DHW) directly off your boiler by means of an Immersion Coil, internal to the boiler? If so your options are very limited. The boiler must be at temperature to produce DHW. Train yourself and users to switch the boiler on and off (seasonally) to produce DHW only when you need it. Don’t let your boiler run all summer to have on-demand supply! A waste of energy. (See other blogs.)
  2. If you generate DHW via a separate, detached water heater of any type and your boiler stays hot when no heat is required (as all summer long?), UPGRADE YOUR AQUASTAT from your current “Ranging Type” (keeping boiler water hot all the time) to a “Cold Start Type” that only warms the boiler when heat is demanded. Our favorite is the Hydrolevel 3250-Plus for oil and the 3200-Plus for gas fueled systems. Note that the additional use of their “Electro-Well” provides Low Water Cutoff (LWCO), a nice boiler safety feature. Nice display, easy to install & adjust; and reasonably priced to boot. Pays itself back in a hurry! Also check out their great videos!
  3. Now, are your aquastat and circulator or zone valves and controls wired properly? They must talk to each other electrically or your boiler runs erratically, zones don’t heat properly and circulators can circulate cold water. The quick way to tell is by removing the Master Aquastat Cover and looking at the “T-T” terminals, usually located near the upper right of the control board. What do you find?
    • If you have only one zone (thermostat) and one circulator, there should just be a pair of smaller wires from your thermostat to the “T-T” terminals. You should be good-to-go, otherwise it just won’t run.
    • If you have two or more zones (thermostats) with a circulator for each there should be a two-wire on the “T-T” terminals from a Multiple-Circulator Control Relay or to EACH of several individual Relays.
      • Case 1: If the wires on the “T-T” terminals are from one of your thermostats, IT IS WRONG! This is the most common condition we find. Someone has added additional zone(s) to your system using a SPST Switching Relay like a Honeywell RA89A, Argo, etc. The quick way to tell is to open the Relay(s) and see if it has terminals numbered 1, 2, 3&4 ONLY. You must use a DPDT Switching Relay like a Honeywell RA845A, Argo, etc. that has terminals numbered 1, 2, 3, 4, 5&6. Terminals 5&6 are not powered and are wired to the “T-T” terminals on the Master Aquastat to call for burner operation when any thermostat calls for heat. Changing them will allow the boiler to run ONLY when calling for heat. Energy and equipment saver.
      • Case 2: If the wires on the “T-T” terminals have a “jumper wire” across them, IT IS WRONG! Your system is running on a “Ranging Aquastat” that just keeps the water temperature in its setting range and from which the circulators pull heating water on-demand. This method is tough on equipment and effectively reduces both the capacity and the recovery of your system. Referring to preceding Case 1 go through the steps with Circulator Relay qualification and inter-wiring to bring the system up to peak, efficient operation.
      • NOTE: If in either Case 1 or 2 you are using a Circulator Switching Relay, or a Zone Valve Control the interior “End Switch” terminals are wired to the “T-T” terminals on the Master Aquastat only. Finished.
  4. If you are using Zone Valves in your system, are your aquastat and zone valves and controls wired properly? The first step is to verify that all of your zone valves have wiring to all THREE terminals (1, 2&3). Next is to trace and verify that there are leads from terminals 2&3 on all valves to the “T-T” terminals on the Master Aquastat. Refer to this Taco Zone Valve Link to verify wiring: NOTE: If you are using a Multiple Zone Valve Control Relay, the interior “End Switch” terminals are wired to the “T-T” terminals on the Master Aquastat only. The 3 (R-W-G) wires from each zone valve and the 2 (R-W) Thermostat wires from each zone are wired to their respective interior relay locations. Refer to this Taco ZVC Relay Link to verify wiring:
  5. If you are using older Taco Zone Valves in your system consider upgrading them, particularly if they have Green-colored Heads (Tops). They were troublesome and Taco upgraded them with Gold-colored Heads. These Zone Valves are typically slow to actuate on & off, use measurable electricity to energize and maintain position and restrict hot water flow in the system. (Consequently we have preferred circulators.) Recently however Taco introduced a new, low power usage Ball Valve to replace these. Check this link: The “Zone Sentry™” does it all well, very well, and with a useful indicator LED. By the way they are also less expensive than the older valves! Why repair it when you can swap it? Their Ball-Porting Design has a higher “Cv Rating”, or effective flow rate and will definitely help out with those slow warm-ups, and lazy zones. Saves the circulator(s) a bit too. A winner all around.
  6. As you replace Circulators, necessarily or not, specify and utilize new generation products only! Recent advances in hydronic circulator and distribution technology are astounding! Despite a higher initial cost, they save lots of energy (electrical & some fuel) and extend service life. Two (2) basic examples. a. Single Circulator System with Zone Valves: Install a Delta-T ECM Circulator ASAP. It’s “thrice the price” but dramatically smooths out energy delivery and radiation pulsation. Swaps out directly with your little green Taco 007 (or other brand). Just attach the sensors to your boiler supply & return piping and go. b. Multiple Circulator Systems: Substitute the Taco 007e Circulator for existing, based on system usage. Again, about “twice the price”, but what a value! Your constant running “system circulator” where used is first, with your following based on zone sizes and usage. Note that radiant heating zones will benefit as well. (Weil-McLain now typically supplies Taco 007e’s only as their residential boiler system circulators. (Taco also documents that the 007e repays itself in 1-1/2 years with energy savings alone!)
  7. Perhaps the best investment a FHW System owner can make is installing an Indirect Water Heater for thermal efficiency and system value/performance. (Refer earlier in this blog and others to “Cold-Start Aquastats” and their benefits.) Don’t care what you are using for a heating fuel, the Indirect Water Heater tops them all in DHW generation. Problem is they are not cheap. You have to be serious about your energy management. There are two methods of getting there, however.
  8. a. The DIY or “Home Brew” Method: Your current boiler MUST HAVE AN IMMERSION COIL FOR DHW. Search out a very good, quality 80 Gallon Electric Water Heater that can be had cheaply, to be used as your storage tank. Strip out all the electrics. The only electrical function to be used is the (upper) thermostat terminals. Procure a Bronze or Stainless Steel bodied Taco 007e Circulator (or equivalent) ONLY! No iron-bodied ones — you are drinking the water going through it. Obtain a DPDT RA845A or equiv. Switching Relay (see prior above in this blog). Plumb a circulation loop from the boiler immersion coil taps to tees at the input and outputs of the 80 gal. water heater. Circulation direction is to the top tee. Wire in the relay as any zone addition, with a two-wire between both “T-T”‘s (relay and water heater). It isn’t a perfect solution, but a cost-effective one.
  9. b. The Professional Method: Applicable to any FHW Boiler configuration. Purchase a quality Indirect Water Heater Unit (we swear by, and not at, the HTP “SuperStor Ultra”). They use boiler water to heat DHW via an internal coil and therefore use iron-bodied system circulators. Other components are similar to the prior above. We would also suggest professional installation of these units. NOTE: Always install a small, correct “Thermal Expansion Tank” on the cold water feed side of any Indirect Water Heater to prevent DHW system over-pressurization resulting from heating that big, cold tank of water!
  10. The final budget item must necessarily be a boiler upgrade. It’s also the point where you should review your heating fuel options. Refer to our extensive Boilers On Demand Heating Blog Library to assist you in this regard. Regardless of your selection, employ top-of-the-line, latest generation appliances! Do your homework carefully but don’t select solely on a prior service relationship basis. The Weil-McLain Replacement Guide is invaluable in this regard! These new, high efficiency appliances are virtually self-diagnosing and trouble-free. Not only the Maytag Serviceman is lonesome these days.

Last Edit: 12/28/2022 PDM

About the Author

Paul Mercier

A Semi-Retired Manufacturing Process Development and Hydronics Engineer.
Following a stellar career in Computer Hardware & Software, Miniature Ball Bearing, Avionics & Panel Meters, Magnetics, Plasma, IC & Discrete Component and Product Manufacturing throughout New England, have re-focused on a second, parallel skill set in Hydronic Heating.
Received U.S. Patent 10,690,356 on an "ENHANCED CONVECTION, DIFFERENTIAL TEMPERATURE MANAGED, HYDRONIC HEATING APPLIANCE". It is America's first, true Hydronic Heating Appliance, enabled by Taco Delta-T ECM Hydronic Circulation coupled with our proprietary near-boiler piping system. The resultant is a simple, durable and efficient hydronic heating appliance that surpasses all contemporary built-on-site systems both in value and performance.

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