Your one-stop guide to central heating motorised valves
Always wanted to know your C plans from your S plans? Your 2 ports from your 3 ports? Yes? Then look no further than this, your Plumberparts guide to central heating motorised valves.
What is a central heating motorised valve?
Motorised valves use electricity to direct the water in central heating systems from the boiler to where it needs to be - either to the cylinder coil to heat the hot water, or to your heating circuit to heat (typically) your radiators.
How does a 2 port motorised valve work?
If the 2 port motorised valve is switched on ("actuated" in plumbing speak) the ports allow the water to flow. If it's off, the flow is blocked
Two port valves are used in S plan and C plan heating systems. An S plan is used in fully pumped systems, whereas the C plan design is for vented gravity-fed systems typically found in older homes.
Watch the video to find out more on S Plan Heating Systems and 2 Port Valves
What about a 3 port motorised valve? How do they work?
There are two types of 3 port motorised valve. Yes, bear with me! The first type is a diverter or spring valve, found in a W plan system. In a Y plan it'll be a mid-position valve, which means it can send hot water to the cylinder (to heat the hot water) - and the the radiators at the same time. How much goes on one or the other depends on who's in control! In our house that's Big G [link to tabby cat here], but for everyone else, it'll be the cylinder thermostat or room thermostat!
A word of warning: you need to be completely competent in electrics before you start fiddling with motorised central heating valves. Isolate the electrics and make sure you use a tester. If you're even 0.000000000001% unsure what you're doing, then call in a pro!
Watch my video: 3 Port Valves and Y Plan Heating Systems
What's the extra white wire in a 3 port motorised valve?
The extra white wire is another type of live: it acts as a signal or switch input for either the heating or hot water circuit, moves the motor round and turns the boiler or pump on. It's a little extra system safeguard so the boiler of pump don't run unnecessarily when there's nowhere for the water to flow to.
Common faults with motorised valves
If your motorised valve isn't working, there's a pretty short list of things that could've gone wrong. Motor failure could be one, a jammed valve would be another. If the motor's given up the ghost then push the lever forward gently to latch it open and activiate the manual override. Then call a plumber! :)
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