halstead finest gold tripping out?

any ideas ? halstead finest gold trips out when hot water on trips out when c/heating on max trips out, but when c/h on min stays on for approx 4 hrs before locking out, removed the thermostat on the boiler stays on a little longer, but hot water will still trip the boiler out, no ohms reading at the thermostat but readings on the termistors for c/h & dhw any ideas?