What's a "normal" setup for motorised valves?

Our house was built in 1987, so nearly 20 years old. A few months ago the CH failed and I traced the problem to the motor on the valve supplying the heating circuit. Replaced motor and all OK.

Now we have the same problem but in reverse: CH works fine but no HW. Can I expect to find another valve somewhere doing the same job for the HW circuit?

What's the average lifespan for these synchronous motors?

Why are they called "synchronous"?

(I suspect I know the answer - it's under carpet under the floor above the boiler but I just need someone to confirm my suspicions!)

You will have either one 3-port valve or two 2-port valves. The 3-port is probably a mid-position valve which sends the water either to the HW circuit, the CH circuit or both. Which do you have?

Synchronous motors are so called because they run at a fixed speed based on the 50 cycles/second (hertz) of mains AC electricity. This makes them very simple and cheap to produce. They normally have a long life, but if the valve is not moving freely this might possibly impose a load on the motor which would shorten its life (not sure about that).

Apart from the motors, the other things prone to fail in motorised valves are the microswitchs. In 2-ports these simply switch the boiler and pump on when a valve opens, but with 3-ports they have a more complicated role in holding the valve in the mid-position. You can find more detail on 3-ports in this recent thread - //www.diynot.com/forums/viewtopic.php?t=62788&postdays=0&postorder=asc&start=0

Thanks!

Sorry to admit that I can't remember. I'll check tonight but essentially you've answered my question:

3 port - check cylinder 'stat.

2 port - up with the floor!

Why do these things always happen at the wrong time? My retired plumber neighbour is away and I'm on an overseas trip next week! Do plumbing systems have a sixth sense?