Honeywell L641 Surface Contact Thermostat Instructions
- June 17, 2024
- Honeywell
Table of Contents
Honeywell L641 Surface Contact Thermostat
DESCRIPTION
The L641 is a surface contact thermostat designed to sense the water
temperature in storage cylinders and water pipes, and to provide temperature
control, temperature limiting, and temperature feedback functions.
L641A mounts directly onto domestic hot water cylinders and can be wired to
directly switch a wet central heating circulating pump, or boiler, or to
operate spring return and motor open/motor close zone valves.
L641B mounts directly onto a pipe and can provide high limit, low limit or
frost protection in wet central heating systems or automatic summer/winter
changeover in XE70 fan-coil control systems.
FEATURES
- Version available for use as a cylinder thermostat in domestic hot water installations
- Version available for use as a pipe thermostat in fancoil applications
- Version available for use as a pipe thermostat in frost protection applications
- Version available for use as a pipe thermostat to limit the supply water temperature in underfloor heating and solid fuel systems
- The S.P.D.T. switching action is accomplished by a snap-action MICRO SWITCH which is actuated by a bimetal temperature sensing element
- The desired temperature control point is set by the clearly scaled temperature selector on the front cover
- Wiring terminals are easily accessible
- Tamperproof temperature setting (L641B)
- Screwdriver slot temperature setting, with optional manual setting knob supplied (L641A)
- CE approved
SPECIFICATIONS
| Supply voltage | 230 V~, 50…60 Hz |
|---|---|
| Switch action | S.P.D.T. Type 1CL |
| Switch rating | 4(2) A, 230 V~ |
| Temperature setting range | see table |
| Differential | Approximately 10 K non-adjustable |
| Surface temperature range | 0 to 95oC |
| Ambient temp. range | 0 to 70oC |
| Mounting | L641A mounts directly onto cylinder using fixing strap provided |
L641B mounts directly onto pipes using fixing springs provided
Dimensions| 44 x 79 x 54mm (1.73″ x 3.11″ x 2.13″) (w x h x d)
Wiring| 3 terminals with wiring clamps, accepting wires up to 1.5 mm2
Approvals| L641 is CE, RoHs and WEEE compliant. For regulatory information,
DoC / CoC number D0005. Product must be wired as shown for CE compliance
DIMENSIONS
**Dimensions in millimetres (inches in brackets)
**
IMPORTANT
- The installer must be a trained service engineer
- Disconnect the power supply before beginning installation
INSTALLATION
Mounting
The L641A cylinder thermostat should be mounted 1 /4 to 1 /3 of the way from
the bottom of the domestic hot water cylinder after removing a section of the
insulation and cleaning the surface.
The L641B pipe thermostat should be positioned less than 0.6 m (2′) from the
boiler, or on a supply pipe to a fan-coil unit, close to the 3-port control
valve.
Wiring
-
Cover removal
-
Wiring to terminals
APPLICATION
| DHW Storage Tanks/ Cylinders (see note 1)| High Limit Underfloor Heating
Systems (see note 2)| High Limit Solid Fuel Systems (see note 2)| Low Limit
Frost Protection (see note 3)| Fan-Coil Unit Summer/ Winter Changeover for
2-pipe units (see note 4)
---|---|---|---|---|---
L641Al039|
·
|
|
| |
L641Bl004|
|
| |
·
|
·
L641Bl012| |
·
|
·
| |
Notes
- The L641A should be mounted 1/4 to 1/3 of the way from the bottom of the cylinder.
- The L641B should be mounted less than 0.6 m (2′) from the boiler.
- The L641B should be mounted on the boiler return pipe and used in conjunction with the T4360A FrostStat.
- The L641B should be set to approx. 25o C and mounted on the supply pipe close to the 3-port control valve such as to sense the water temperature even when the valve is closed.
Water Temperature Sensing and Control
D.H.W. Storage Cylinders and Tanks **
**
Limit Control in Pipes
High Limit For Underfloor Heating For Solid Fuel Systems
Low Limit For Frost Protection of Exposed Pipework
SUMMER / WINTER CHANGEOVER FOR 2-PIPE FAN-COIL UNITS
WIRING DIAGRAMS
L641A1039 DHWS ControL
Terminal 2 used on Honeywell Y-Plan systems
Heating Load
Heating Load
L641B1012 High Limit
Heating Load and existing controls
Contacts C and 1 break on temperature rise
**L641B1004 Low Limit (Frost Protection)
**
**L641B1004 Automatic Summer/ Winter Changeover XE70 series Typical wiring
**
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