Raymarine Heading Data Lost — Compass Sensor Fix

What it means

Raymarine 'Heading Data Lost' (or 'No heading data') means the plotter is no longer receiving a heading from a compass sensor on the network.
Heading is what aligns the radar overlay, makes MARPA target tracking work, and lets the autopilot steer a compass course — so several features stop at once even though GPS, chart, and depth carry on fine.
The source is usually the heading sensor (an EV-1, a fluxgate, or a SatCompass) or its connection to the backbone.

Affected Models

Raymarine Axiom / Axiom Pro using radar overlay or MARPA
Raymarine eS / gS Series with an Evolution EV-1 or fluxgate compass
Systems with an autopilot supplying heading to the network

Common Causes

Heading sensor (EV-1, fluxgate, SatCompass / GA150) lost power or dropped off SeaTalkng
Autopilot course computer that normally relays heading went into standby or lost power
Loose or corroded SeaTalkng spur at the sensor
Backbone fault — missing terminator or a T-piece pulled apart
Heading source set to a device that's currently switched off
Failed compass sensor

How to Fix It

Check the heading source setting.

Go to the data source settings and find Heading.
If it's pointed at a device that's switched off — say an autopilot you didn't turn on today — the plotter has no heading feed.
Switch that device on, or repoint heading at whichever compass sensor is actually live.
Check the heading sensor's power.

Find the heading sensor — on Evolution systems it's the small EV-1 box, often near the centreline low in the boat.
It draws power from its SeaTalkng spur.
If that spur or the backbone it hangs off has lost power, the sensor goes dark.
Reseat the spur connector and confirm the backbone power tap is live.
Check the autopilot, if it supplies heading.

On many boats the autopilot course computer is what puts heading onto the network.
If the pilot is off or has lost power, heading disappears with it.
Power the autopilot up — it doesn't need to be engaged, just alive — and heading should return.
Inspect the backbone.

A SeaTalkng backbone missing a terminator at one end becomes flaky and devices drop in and out.
Walk the run, confirm both ends are terminated and every T-piece is fully seated.
This is worth doing whenever any single device keeps disappearing — the backbone is the common factor.

Frequently Asked Questions

Why did my radar overlay suddenly go wrong instead of just disappearing?

If heading is lost while the radar is still running, the plotter can't rotate the radar picture to match the boat's direction — so the overlay smears or sits at the wrong angle instead of vanishing outright.
Restore heading data and the overlay snaps back into alignment.
Until then, use the radar in its own un-overlaid (head-up) window, which doesn't need heading.