The new DU144 automatic bypass valve from Honeywell provides a reliable and cost-effective means to satisfy the boiler bypass requirements of Good Practice Guide 302, part of Building Regulations Part L1 in England and Wales.
It has a unique and simple adjustment mechanism that increases water flow automatically according to the water pressure across it. So, as rooms reach desired temperature and valves (zone valves, thermostatic radiator valves or manual valves) close, the DU144 opens proportionally to enable safe water flow around the boiler. When valves reopen, so decreasing differential pressure, the DU144 closes and flow is redirected from the bypass to the heating loop.
The DU144 improves the efficiency of the system compared with a fixed bypass because bypass flow is minimised when thermostats are calling for heat.
Good Practice Guide 302 states that a bypass circuit including an automatic bypass valve must be installed if the boiler manufacturer specifies that a minimum flow rate be maintained while the boiler is firing.
It is easy to set differential pressure on the DU144, even in low light conditions, by turning its knurled handwheel against high-visibility markings on the stem.