VMB4RY relays stuck

I have a vmb4ry which has 3 of the 4 relays on it working my oil heating and associated zones. Noticed this morning that the oil heater would not turn on, so went checking the basics etc. Checked the relay was working, and power was being delivered etc,and all looked ok. After a bit more investigation, I noticed that all the relayoutputs were presenting 230v on the output, irrespective of relay status (ie when relay was off, still getting 230v on the output), so the relays seemed to bestuck in the "on"position.

It seemed odd, as I could hear the relays clicking on and off, but the voltage remained present irrespective of status. I powered off the 15v to the vmb4ry and on again, and got the same result. Only after removing the 230v input to the relays did the problem clear and the relays return to normal operation.

Now a bit frusrating, as it seems my oil has run low, so the burner must have been running for some time!

Has anyone experienced this issue with the vmb4ry before? I am worried it may happen again, especially with something as critical as heating, as the cost implications are huge, and it can go completely un noticed!