No CH unless hot water on

Edward H wrote in news:e79db$58286e21$a2d350aa$ snipped-for-privacy@news.flashnewsgroups.com:

On many systems the boiler is switched by the motorised valve contacts. ie. When the water valve closes a contact will get made to power the boiler through the room stat. My first place to look would be at the micro switches to ensure the valve is actuating them.

Room thermostat not calling for heat? If a wireless model check that the battery isn't failing in the room stat - the display may still be active but not enough power for the RF to transmit to the receiver.

That doesn't compute.

I think depending on how its done, this is a motorized valve issue. It looks like the valve is doing its thing, but its not firing the boiler.

replying to alan_m, Edward H wrote: Thanks. I have a tado system fitted which appears to call for heat but nothing happens. Perhaps there is fault in wiring that gets power to the valve/switch as have tested switch and valve motor and they are ok

Yes - either a microswitch has died, or the valve isn't moving far enough to operate them.

The OP says he's got a "two zone port valve" and it's that that dosn't compute. If he means a two port zone valve, then there will probebly be a second one somewhere to control the DHW and if the cylinder stat is calling for heat then latching the CH one open will heat the radiators, The fault could be the valve, but equally a stat or wiring fault.

Maybe he's got a single three-port valve (FX: shrug)

Is it "doing its thing"? The OP is manually moving the valve which suggests that it may not be driven to the position when CH is selected.

Not being driven to the CH position and the boiler not firing suggests that the thermostat is not switching the power. Regard the thermostat as simple on/off mains switch.

replying to alan_m, Edward H wrote: Thanks. There is another valve above the two.port valve . I don't think power is getting to the two port valve which makes me suspect wiring or thermostat fault. Wish I knew how to fix it!

Have a look at:

It has all the common wiring plans and valve combinations.

You need to follow the system through in logical steps. So first check that the stat is generating a call for heat. Then check it reaches the valve. Then that the valve moves, and lastly that the microswitch on the valve sends a call for heat to the boiler and to the pump. If any in that chain fail, you will not get any CH.

Very unlikely - the boiler probably only has one input and it will be used for both CH and DHW. So if it works for one, the fault on the CH will likely lie elsewhere.

Manual for the boiler here:

replying to John Rumm, Edward H wrote: Thanks John. I hear a click when heat called for but don't know whether it comes from the 2 port zone valve or the similar looking valve above it which has no manual switch on it . No idea what that one does! I feel am getting close thanks to everyone s help. My best guess is fault is somewhere between stat and valve

If you have a multimeter, then it should be easy enough to track down looking at the voltages on the control wiring. See if you can find the wiring centre or junction box where all the components are wired together. If it worked in the past, and does not now then the most likely candidates are:

Post some photos somewhere we can see them, and we may be able to give some more pointers.

replying to John Rumm, Edward H wrote: Thanks John. Its digital. Have thrown in the towel and called plumber! Will let you know what he finds.

There are some CH wiring configurations that only allow you to have CH on when the HW is also on. I don't think you need to use that kind of wiring with two zone valves, but there is sometimes (maybe always) a little DIP switch in the timer to tell it that that is what you have. Maybe that is switched incorrectly?