Honeywell / Resideo L8148 Aquastat Controller Features & Installation

Install, Wire & Set-up L8148 aquastats

L8148 Aquastat Uses

This Honeywell / Resideo aquastat

• Is used with a 24VAC thermostat
• Provides a high-limit control that is set using a dial with settings in the range of 180F to 240F (82C to 116C) with optional models available with a scale range of 140F to 240F (60C to 116C)
• Uses a differential that is not adjustable
• Includes models supporting addition of a remote low limit temperature control
• Includes models that can operate 2 zone valves or 4 relays such as the Honeywell R8320C. To add additional relays you'll need to add an additional transformer to power them in groups of 4.

This page describes the features of the L8148 and provides links to installation manuals for its various models.

For troubleshooting this control see our sister article

at AQUASTAT L8148 AQUASTAT INSTALLATION

Note: In 2018 Honeywell announced that Resideo would be the corporate name of the Honeywell Homes product portfolio and ADI global distribution businesses when they became a stand-alone, publicly traded company following completion of a spin that was expected by the end of 2018.

Honeywell L8148-series aquastat model differences

Honeywell offers aquastat controllers for both oil and gas fired heating equipment such as hydronic (hot water) heating boilers and water heaters. Both single function (high limit or low limit are separate controls) and multi-function aquastats are provided.

The photo shows a Honeywell L8148E installed on a gas fired heating boiler, courtesy of reader Paul, July 2018. The data tag on the aquastat interior (red arrow) can help identify which version of the L8148 Aquastat is installed.

The Honeywell L8148 series aquastats are used on hydronic heating equipment and use an immersion-well sensor to inform the aquastat of the boiler temperature.

• Honeywell L8148A aquastat switches line voltage to the burner, mounts horizontally, contains a HI limit only, uses a 24VAC thermostat.
  
  This control model has no adjustable DIFF or differential control. The control will turn on both burner and circulator on a call for heat at the thermostat, and will turn the burner OFF when the boiler temperature exceeds the HI or high limit.
• Honeywell L8148A-1017
  
  is a horizontal-mount aquastat with a 8deg DIFF control. The controller switches both burner and circulators.
• Honeywell L8148E-1265
  
  is a vertical-mount aquastat with a 15deg DIFF control using a 24VAC transformer. Its high limit opens the burner circuit only. A remote low limit controller can be added.
• Honeywell L8148E-1299
  
  is a vertical-mount aquastat with an 15deg DIFF control and a 50VAC transformer. The limit control can switch both burner and circulator. This unit is designed for a low-voltage burner circuit.
• Honeywell L8148J
  
  is a vertical or horizontal-mount aquastat switching a millivolt circuit (such as found on gas control valves)

Often an alternative case is available to convert vertical to horizontal mount for these controllers.

A link to the Installation and Operating guide and cross reference manual from Honeywell is give in the article references section.

IF voltage is being supplied to the burner (to turn it on) and the burner never runs, the the problem is probably not the aquastat but the burner itself, such as a burner that has tripped off a cad cell relay or other safety control.

See details

at OIL BURNER WONT RUN 

or on an LP or natural gas burner system the burner is turned on by a low voltage circuit

Gas burners on a heating boiler typically used a Honeywell L814B like the L8148E1257/B that has an isolated burner circuit typically used with powerpile systems. That aquastat is replaced by the L8148J1009/U Aquastat Relay, a universal replacement offering 120 – 240 F range with 8 degree F fixed differential, low volt/millivolt

See gas fired boiler troubleshooting details starting at

DIAGNOSE & FIX HEATING PROBLEMS-BOILER  at https://inspectapedia.com/heat/Heating-Boiler-Diagnosis.php

Same diagnostics and same electrocution shock warnings as above.

High & Differential Settings/Values for the L8148 Aquastat

L8148 Aquastat HIGH Setting

On all heating system aquastats, the high limit switch shuts off the burner when the boiler temperature exceeds high-limit setting.

For the L8148 aquastat HIGH LIMIT Setting,

• The Standard Scale Range: 180°F to 240°F (82°C to 116°C).
• The optional operating range is 140°F to 240°F (60°C to 116°C)

For this aquastat, to set the HIGH LIMIT, remove cover, and turn dial until the desired setting is directly below the pointer.

OPINION: for efficiency we usually like to operate heating boilers at the upper end of their range, setting the HIGH LIMIT close to 200F.

Watch out: We don't go above that temperature because overheating risks spillage at the pressure/temperature relief valve - then creating a safety hazard.

A "dial stop" in this control prevents turning the temperature limit above a fixed point set at the factory. That stop can be changed, but for most installations we do not recommend doing so.

Quoting from a typical L8148 instruction manual,

The dial stop is factory-set at the high end of the limit scale. To adjust, use a small screwdriver to hold the stop away from the dial face, and turn the dial until the desired setting is below the pointer. See Fig. 8. Release pressure on screwdriver, and make sure the stop rests flat against the dial face.

L8148 Aquastat DIFF Values

As we show below, the DIFF or "Differential" settings on the L8148 series aquastats is fixed. It is not adjustable.

That means that when the boiler temperature drops a fixed number of degrees F below the HIGH limit dial setting, the aquastat will turn on the burner (provided there's a call for heat).

The illustration below, adapted from a different aquastat, is used here as the 8148 manuals don't include this drawing. It generally correct for the L8148 as we'll explain.

At AQUASTAT CONTROLS, our home page for this control, we explain in more detail, from which I excerpt:

The boiler Cut-on temperature or burner turn-on temperature for the boiler, AS LONG AS THE THERMOSTAT IS CALLING FOR HEAT is fixed at 10 deg. F. in this drawin which is for a different aquastat: the R8182D.

But for the L8148 Aquastat, the DIFF or TURN-ON temp is fixed at a temperature below wherever the HI is set.

(Green in our edited version of Honeywell's drawing.)

From the table below you'll see that for some L8148 controls this hard-wired fixed gap is 15 °F.

While on other L8148 controls this hard-wired fixed gap is 8 °F.