Hot water comes on if heating on. But doesn't work on it's own

Just installed a Tado wireless thermostat, internet bridge and wireless receiver. The hot water works ok when the heating is on. When i put hot water on seperately, it tries to start but eventually the boiler just trips out and i have to reset it. The boiler is a Worcester Bosch Greenstar ri. I am thinking the 3 way valve is not opening, that is why the boiler is tripping. Everything worked fine with the old system though, so suspect a wiring problem. Am waiting for support to get back to me. Any ideas?