Just had a call from my daughters who are complaining that the shower in their flat is running hot and cold. The boiler is a bosch worcester and the shower a mira mixer. The boiler was serviced in june before we bought the flat and has performed ok up until now. I'm just back from having a look and after going through the installation manual and check list I'm not to much sure what the problems are. The boiler is heating the water OK and actually faster than the shower can use it,however there is a part during the test that says to reduce the water flow and see if the gas flow reduces and the temp stabilises at 58 degrees. It doesn't seem to do this and through the burner window I can't visually see the flames change height or intensity. I therefore assume that it is the overheat thermostat that cuts out the boiler.
At this point it says to check the resistance of the modreg solenoid coil and it's spot on at 120 ohms. It also says to check the spindle rotation which I cant seem to do as there is a screw with a red head and a gas pressure set at factory sticker on it (so I left it alone ). The hot water sensor is working within its resistance range as well. So I reckon It's either this gas valve spindle which will need a corgi reg or the main driver board is not telling the gas valve spindle to cut back on the gas to stabilise the temp. The only thing I ain't done is take the control panel to bits and check all is OK there ( job for next weekend prob). Would anyone care to pass coment on my findings sorry about the long post folks.
By the way is the spindle on the gas reg valve like a stepper motor type thing and would i be able to monitor/meter it to see if the driver board is sending it a signal.