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Problems with Watchman Sonic? Troubleshooting and help

Here are a few tips if you’re having problems with your Watchman Sonic.

Here is a download of Watchman Sonic Instructions.

Here is a download for the red Watchman Sonic Alarm Instructions.

No signal on Watchman Sonic gauge

From time to time the signal of the Watchman Sonic can cut out. For example, this can happen in a power cut when the tank has been topped up or due to bad weather. This is indicated by an exclamation triangle with no bars displayed. First of all, it’s best not to panic as this can simply be down to the receiver plug losing connection to the gauge or alarm unit on the tank. The gauge will attempt to reconnect automatically.

If the gauge does not reconnect automatically then follow these troubleshooting steps.

There are a few simple steps to re-calibrate the gauge if it stops reading the oil level of your oil tank.

Pairing Transmitter and Receiver

  1. Unscrew the green transmitter disc (or red if it is an alarm) from the top of the oil tank. On a bunded tank, Sync Watchman Gaugethe gauge is located inside the lid on the inner tank.
  2. Take the transmitter disc to the white receiver which should be plugged into the mains in your home.
  3. Align the black dot on the right-hand side of the white receiver plug with the grey dot on the disc; the bars should start appearing one by one, once it’s flashing and beeping the sonic gauge has been calibrated. This can take 20 seconds so be patient. See picture ->
  4. After the disc has been synced with the receiver take the disc straight back out and fix it to the tank.

Watchman Sonic not reading correctly – how to update Watchman Receiver

If an incorrect level is being shown on your oil monitor then it’s worth checking that you have measured the height of your sensor against the tank correctly. 3 metres is the maximum height for the sensor from the base of the tank. Make sure that you are only measuring the internal depth of the tank. Do not include the outer skin of bunded tanks in your measurement and take the measurement from no lower than the maximum fill level of your tank.

Change Sonic battery: battery model Varta CR2430

Check first whether your Watchman Sonic Unit is in warranty or not. Opening a Watchman will void the warranty if it is still in effect.
The battery on the Watchman Sonic lasts for approximately up to 5 years.  To replace it, follow these instructions:

  1. Switch off your Watchman display in the house.
  2. Remove the transmitter from the tank and take transmitter indoors, into a clean dry environment
  3. Using a cross point screwdriver, undo the four screws located under the main body of the transmitter
  4. Remove the top cover
  5. Flip out battery ( be careful not to break the retaining clip )
  6. Clip-in the new battery
  7. Re-fit top cover
  8. Evenly and gently tighten all four screws – do not over tighten
  9. Replace the green or red disc on the tank
  10. Switch on Watchman display in the house and wait a minimum of 10 minutes for the oil level to refresh
Where can I get a CR2430 battery from?

Most online retailers will stock them. Usually, they can be bought fairly cheaply from Amazon.

The standard warranty on a Watchman Sonic gauge

The warranty period on a watchman oil level monitor is 12 months. In order to find out if your unit is still under warranty look on the back of the receiver for a 6 digit number. This can be found underneath the Part No. “A45-2817” is an example of what this might look like. The last 4 digits depict the month and year that it was issued. If the current date is within 12 months of that printed on your receiver then you should contact or call 028 3836 4415. Otherwise, we will be happy to help!

Other error messages:

Watchman Gauge Display Icons

Watchman oil monitor flashing triangle errors:

Oil Tank level displayed with an exclamation mark in a triangle = battery low

Replace the battery as detailed above. The Varta CR2430 is the standard coin battery for these gauges.

No level and an exclamation mark in a triangle = transmission not heard

This means that the plug-in receiver can’t receive a signal from the transmitter on the tank. This can clear up by itself after a couple of hours and tends to show when the receiver hasn’t got a signal for a while.

If the problem persists, pairing the receiver and the transmitter (green or red disc) on the tank may resolve the issue. This process is detailed above.

5th (middle) bar lit with an exclamation mark in a triangle = no echo condition

This means that the green or red Watchman disc is having trouble receiving the radar echo from the bottom of the tank.

The Watchman Sonic works by firing a beam of radiowaves down into the tank. These waves then bounce off the oil, the watchman measures the time it takes to receive the “echo” back which it uses to calculate the oil level.

If there any objects or debris in the way of the beam then this error may occur.

  • Check the oil in the tank is clear from any debris such as twigs or any dipsticks
  • Remove the transmitter disc from the top of the tank and check to make sure the cone on the bottom of the disc is clean and clear of any white residue (oil sweat)

If neither of these steps clears the error after refitting the disc and waiting for the gauge to send a new signal, it is possible that the gauge has been installed incorrectly.

This could mean that the gauge has been installed at an angle and not pointing straight down into the tank causing the beam to bounce around the tank and not be received correctly.

Alternatively, the gauge has been installed in a location where there is a ‘window’ in the inner tank. This window would block the beam before it reaches the oil.

Sonic not displaying correct oil level.

Occasionally, your Watchman Sonic can show a full tank level, even if the level is lower.  This can be due to the acoustic sensor being blocked or partly blocked.  A simple fix for this is to remove the green (or red on Alarm units) sender head unit, on the tank, by unscrewing it from the base plate. This requires no tools. Once removed, wipe out the underside of the transmitter with a soft cloth or kitchen towel. This will remove any white powder build-up and moisture.  Refit the sender and wait for the signal to update (up to an hour).

If none of the above tips help, it may be time to replace the gauge. We have the Watchman Sonic available from stock for quick delivery.

Or you may like to upgrade to the Watchman Sonic Alarm – Which can be fitted to the existing transmitter base for a quick installation.

You can view all our oil tank gauges to purchase on-line here.


Historical Warning Indicators

  • F = full
  • Red light flashing with no level = no signal
  • Fluid level low and ‘’BAT LOW’’ = new power tube needed
  • C = connection fault replacement needed


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