Guide to the Watchman Sonic, which we fit for free as part of our oil tank installations

Watchman SonicRegular monitoring of your heating oil tank and understanding your oil usage are essential for planning future oil purchases to minimise heating costs and to avoid running out of oil. However, nothing can be more unpleasant than having to regularly go outdoors and check the oil level of an outside tank on a freezing day in winter. Without regular checking, oil consumption can sometimes be much higher than you think (for example, when temperatures are low or if there is an oil leak) and you may be forced to pay a huge price premium by having to make an emergency order from an oil supplier. We fit Watchman Sonic wireless oil tank gauges to all the oil tanks we install at no extra charge. This article describes the Watchman Sonic and how it works.

For those who rely on manually checking their heating oil level, the Watchman Sonic is an amazing, revolutionary electronic device that accurately measures how much oil there is left in your tank. It communicates this information wirelessly to a convenient device in your home. With it, you’ll be able to monitor your oil usage from the comfort of your own home and never run out of oil again! By accurately monitoring your oil usage, you’ll be able to minimise the annual cost of your heating oil.

Correct installation is essential to providing accurate measurements and avoiding damage to your oil tank or invalidating its warranty. We take care of all the installation for you as part of our fully-guaranteed oil tank installations.

With many tanks, drilling is required to fit the Watchman Sonic transmitter, which is why we advise you to leave this job to the professionals rather than trying to fit a Watchman Sonic yourself. The Watchman Sonic transmitter has to be properly fitted to a correctly-installed tank to provide an accurate reading. The tank the Watchman Sonic is to be fitted to has to be on a flat level base, be within a 200-metre range from the receiver position and have a maximum tank height (not including the base) of 3 metres.

The drilled hole must have a minimum 30mm diameter, and the space beneath the Watchman Sonic transmitter should be free of any obstacles so that the ultrasonic beam path is clear of obstructions. The drilled hole should be on a flat level point that is at the same level and no higher than any opening at the top of the tank (such as the filling point). It is essential that the transmitter does not sit at an angle, as this would give a incorrect level reading. The Watchman Sonic transmitter should not be installed on an area on which water could gather.

Once the transmitter has been installed, the receiver should be correctly installed, making sure that the special switches are set properly, according to your specific tank. We will do this all for you.

Once installed, the Watchman Sonic receiver provides a simple visual indication of your oil level. It provides a bar graph level display, with 10% tank height per bar. An early warning indication (a flashing tank fill icon) is given once the oil level reaches a predetermined height above the bottom of the tank. When the oil reaches a very low level, a tank empty warning flashes.

Here’s a video guide for the Watchman Sonic:


There is an optional upgrade to Watchman SENSiT, allowing you to get oil level notifications directly to your mobile phone.

The Watchman Sonic is usually very reliable and will operate without problem. Batteries typically last for about three years. A replacement battery can be purchased from many retailers. The battery model is the widely-available CR2430. Battery replacement is very simple. Just remove the transmitter from the tank and bring indoors. Undo the four screws and remove the top cover. Flip out the old battery, clip in a new battery and refit the cover. Tighten all four screws and replace the transmitter on the tank. That’s it!

We supply and install affordable oil tanks across Cambridgeshire and East Anglia, and won’t be beaten on price. We include the professional installation of a Watchman Sonic gauge at no extra cost. For a no-obligation quote, please contact us now.


For more information about our oil tanks, visit:

Oil Tank Replacement in Cambridgeshire and East Anglia

A Fireproof Oil Tank Allows Placement Adjacent to Buildings and Boundaries

Choosing the Size, Type and Placement of an Oil Tank and the Importance of Planning Regulations