Myson Apollo gas boiler and pumped CH system. Room thermostat in entrance hall. HW and CH work fine when switched on and (usually) switch off appropriately. About three times per year, when time switch goes to "off", the pump continues to run, and the boiler cycles ineffectively (and noisily) against the now closed motorised valves. The valves work fine. After a few weeks of sleepless nights, it seems to fix itself. Any ideas on how to fix it myself?