False signals from sensor - help please

So... woken at 4.42am this morning with back door sensor not responding.  

Also had games room entry sensor open last week.

I decided to run a test.

GAMES ROOM

Sensor showed window OPEN when closed. Note window had not been open for months.

I set system to home mode. Refreshed it. Still said open. So it will obviously ignore this window (if it was open).

I opened the window (closed but system in error thinks its open) and the alarm immediately sounded.

Outcome - entry sensor sending signal to base saying it's open but sensor is operating in responsive state and when open it the alarm sounds.

BACK DOOR ENTRY SENSOR (add multiple others)

Signal - entry sensor not responding.

I have my sirens set to beep when an entry point is open in off mode.  

So with it not responding I opened the back door.

Outcome- siren beeped to state back door had been opened.

CONCLUSION

The sensors - multiple sensors- are all stating the system is not responding yet they ARE responsive.

Has anyone had this problem before and able to help?