The hot water is fine, but the radiators are not heating up


The boiler is working, you get hot water, but the radiators stay cold.

Likely Cause

  1. The wall thermostat in the hall is turned too low.
  2. A problem with the time clock.

What you can do

  1. Check the wall thermostat in the hall (See Managing the system on the general Heating page.)
  2. Check the time clock on the side of the tank.
    There are 3 common things that can be wrong:
    a) It is set to the wrong time. (This can happen if there has been a powercut, for example.)
    b) The little switch in the middle has been set to ‘Off’ instead of the middle ‘Auto’ position.
    c) All the time setting pins are set to the inner ‘off’ position.

If this does not work

There is probably a fault with either the timer mechanism, one of the pumps, the valve that directs the water into the radiator system or the electronic board that controls the system. You will need to get a professional plumber to diagnose and fix it.

Extra Tip

If the fault is with the mechanism that turns the timer, you may be able to get some heat until it is fixed by setting the little switch in the middle to be permanently ‘On’ and making sure that the wall thermostat is set to a high temerature.

The original timers were made by a company called Grasslin. Replacement mechanisms are easily obtainable and slide in and out of the plastic box that houses the timer. They must be compatible in size and function.

Grasslin timer guide (pdf 155Kb Right-click and ‘Save As…’ to download)