CENWAT System Controls and Zoning 2

Question 1

In a Y-plan fully pumped heating system, which type of motorised valve is used?

Accepted Answer

One 3-port mid-position valve

Answer

A Y-plan system uses a single 3-port mid-position valve that can direct flow to heating, hot water, or both circuits simultaneously.

Question 2

What is the key operational difference between a 3-port mid-position valve and a 3-port diverter valve?

Accepted Answer

A mid-position valve can supply both circuits simultaneously; a diverter valve cannot

Answer

The mid-position allows hot water to flow to both the central heating and hot water cylinder at the same time, whereas a diverter valve can only supply one circuit at a time.

Question 3

In an S-plan heating system, how many motorised valves are typically installed?

Accepted Answer

Two 2-port zone valves

Answer

An S-plan system uses two separate 2-port zone valves — one for the central heating circuit and one for the hot water cylinder — providing fully independent control of each zone.

Question 4

What is the function of the end-of-travel (auxiliary) microswitch in a motorised zone valve?

Accepted Answer

To prove the valve is fully open and complete the circuit to fire the boiler

Answer

When the valve reaches fully open, the end-of-travel microswitch closes, completing the low-voltage circuit that energises the boiler, ensuring the boiler only fires with an open valve.

Question 5

What happens when a 2-port zone valve closes because its thermostat is satisfied?

Accepted Answer

Power is removed from the motor; a spring return closes the valve and the auxiliary switch opens, removing the call for heat

Answer

When the thermostat is satisfied, the motor is de-energised; a spring return closes the valve and the auxiliary switch opens, removing the call-for-heat signal from the boiler.

ACS CENWAT Practice Test

ACS CENWAT Practice Test

CENWAT System Controls and Zoning 2