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Honeywell Home 22mm Automatic Bypass Valve | DU144A1001
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£59.70
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£49.75
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The Honeywell Home DU144 22mm Automatic Bypass Valve (part code DU144A1001) is a straight-pattern, brass automatic bypass and differential pressure valve for wet central heating systems. Fitted in a bypass between the flow and return pipework, typically at or near the boiler, it keeps the minimum flow rate your boiler needs while it is firing, even when thermostatic radiator valves (TRVs) or zone valves have closed down the main circuit.
Because it is fully automatic, the valve stays closed while the TRVs are open and only starts to open as differential pressure across it rises. That means water is diverted through the bypass only when it is needed, rather than constantly, as it would be with a fixed-position valve. The result is steady flow through the boiler, quieter operation where excess water velocity causes noise, and a higher boiler return temperature that helps reduce flue gas condensation corrosion.
Supplied with 22mm compression fittings for copper tube on both inlet and outlet, it is factory set to 0.2 bar and can be adjusted from 0.1 to 0.6 bar with the handwheel and indicator scale to suit the boiler minimum flow and available pump head. A red protection cap covers the setting once commissioned.
0.1 - 0.6 bar
Adjustable setting range
0.2 bar
Factory setting
kvs 2.3
Flow value (cv 2.7)
10 bar
Max operating pressure
2 - 110 °C
Medium temperature
22mm
Compression, straight
Regulatory and safety information
A bypass circuit must be installed if the boiler manufacturer requires one or specifies a minimum flow rate while the boiler is firing, so always check the boiler instructions first. Where a bypass is needed, an automatic bypass valve is the recommended choice over a fixed-position valve. Any work on or commissioning of a gas boiler must be carried out by a Gas Safe registered engineer.
Compatibility and system conditions
Suitable for water or water-glycol mixtures to VDI 2035 quality with a pH of 8 to 9.5. Maximum medium temperature is 110 °C and maximum operating pressure is 10 bar. This version is for 22mm copper pipe using the supplied compression fittings.
Commission before you set
Commission and balance the heating system first and note the selected pump speed. Use the boiler minimum flow requirement, the pump curve and the DU144 setting chart to find the optimum setting, then turn the handwheel until its lower edge lines up with the matching mark on the stem.
Key features
Automatic modulating action
Opens progressively as TRVs close and closes again as they reopen, redirecting flow between the bypass and the heating loop with no external controls required.
Wide, finely adjustable range
Differential pressure is adjustable from 0.1 to 0.6 bar (1.45 to 8.7 psi) using the handwheel and indicator scale on the bonnet.
Factory set at 0.2 bar
Arrives preset to 0.2 bar (2.9 psi), giving a sensible starting point before fine tuning on site.
Protected setting
A red protection cap covers the preset, helping prevent inadvertent adjustment once the system is commissioned.
Quieter, longer-lasting boilers
Helps reduce flow noise caused by excess water velocity and hinders boiler corrosion by raising the return temperature.
Robust brass construction
Brass housing, fittings, bonnet and handwheel, a stainless steel spindle and spring, and NBR and EPDM seals for long service life.
How it works
The DU144 is installed between the flow and return pipework. The differential pressure is set according to the minimum flow the boiler requires and the pump head available. When TRVs close and the differential pressure reaches the set value, the valve starts to open, and as pressure rises further it opens wider to increase bypass flow. When TRVs open again, pressure falls, the valve closes, and flow returns to the heating loop. The valve works equally well on systems with stored hot water and with combi boilers.
Using an automatic bypass valve is also part of CHeSS (Central Heating System Specifications) best practice for domestic central heating, and it becomes especially valuable on systems with large numbers of TRVs.
Technical specifications
Frequently asked questions
BTU & WATT Calculator
Room Dimensions
Room Type
Living Room
Bedroom
Kitchen
Bathroom
Conservatory
Hallway
Glazing Type
Single Glazed
Double Glazed
Triple Glazed
External Walls
0 Wall
1 Wall
2 Walls
3 Walls
4 Walls
Insulation Level
Poor
Average
Good (New Build)
Required Heating
0
Watts
0
BTUs
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