No hot water honeywell st6400c

Possible cause of lockout: boiler low water level. If you have a combination temperature/pressure gauge, it should read approximately 12 psi when the boiler is cold. When it runs, it will be approximately 22 psi. If the pressure is low feel the inlet water supply piping. Open the manual feeder valve. The cold water coming in will verify that there is no obstruction to the water flow. You may have "dirt" in the line. You may have a defective water pressure valve or check valve. Another thought. Make sure your AIR SEPARATOR is functional. Remove the cap and depress the valve. You should see water. If air comes out, continue to"bleed" the AIR SEPARATOR. You may haven't to replace the A/S.

Have had a lot of these programmers with this fault.Integral fault with electronics.Programmer will need to be replace as unrepairable.You should be able to find a straight replacement version from your heating supplier.

Yes it could be something other than the motor but I think you are right yo start there.Good luck and thank you

This does not sound like a thermostat problem. I would be looking for a zone valve or circulator pump problem.

Honeywell ST6400C
Times set on thermostat does not turn on or off the heating or hot water at the set times, but any time of the day

with y plan 3 connections on programmer HW on HW off CH on HW on to cylinder stat then HW call to Orange on Mvalve to power boiler and pump HW off to grey wire on Mvalve to close hot water CH to room stat common then heating call to white on Mvalve

some digital thermostats do no not work with zone valves is this a new thermostat that you had installed

Check how all three "on/off" sequences are programmed firsrt, then all other programmable options. Make sure sliders are in the sliders are in the correct possition. If it becomes more complicated than launching a space shuttle, reset it. Unless your house is a mansion keep it simple with just day and night modes. the money you save wont even cover the cost to fix the hole you punch in the wall trying to do fancy programming ;-D

do you have a separate or built in programmer? if itis separate ISOLATE MAINS undo the screws on the bottom of programmr and checkthat ther are no loose wires ( make a note of where they go for future ref. ). If wires OK check that the valves are working switchoff HW and Heating switch one on at a time and check that each valve is opening and closing and that the boiler and pump fires up ( it could b the micro-switch in the valve is broke! )

Hi yes sound like it not working on hot water only it would check ou the wiring on this side