Salamander CT80BU pump has been in place and working since December 2016 but for the last two weeks it has suddenly started firing up when all outlets are closed, it's not regular either, sometimes won't fire for hours, then others it will fire a couple of times a minute. I think I have ruled out a leak because the pump fires even with the outlet pipes closed at the anti-vibration couplers. I'm 90% sure the issue is on the hot water side but it's very hard to be sure which side is firing. I've also tried running the supply with the pump off i.e. just gravity fed, to try and clear any air but this has had no effect, and have made sure the filters between the pump and couplers are clean. Anyone have a suggestion for what might be wrong?