Downstairs heating only working when upstairs is on

[rich19754]

Hi all - I have a 2 zone heating system with upstairs separate to downstairs and 2 thermostats (one upstairs and one downstairs). When i turn the downstairs thermostat on it clicks and opens the motorised valve but then no demand is requested from the boiler and the heating doesn’t come on. When I then go upstairs and turn the upstairs thermostat on the upstairs rads come on as usual but now the downstairs also works. So far I have replaced the downstairs thermostat (existing was Honeywell DT1) with a Honeywell DT2 and I have replaced the full motorised head with a replacement 2 port Honeywell head but the problem still persists. Any ideas really appreciated as I was thinking of replacing the upstairs head as well but I am not really sure why

Thanks in advance as am at a loss and wondering if the whole valve needs replacing and not just the head maybe

Sorry also it’s a gas combi boiler (vogue C40)

 

[Murdochcat]

Has it ever worked properly?

Randomly replacing parts isn’t a great way to fault find

 

[rich19754]

Hi - yes it worked fine until a few weeks ago.

I could hear the downstairs motorised valve buzzing so was sure replacing that and the thermostat would solve it!!

Agree that randomly replacing parts is no good but as the valve was buzzing and was 18 years old I figured I would just do it

 

[fixitflav]

Hi - yes it worked fine until a few weeks ago.

I could hear the downstairs motorised valve buzzing so was sure replacing that and the thermostat would solve it!!

Agree that randomly replacing parts is no good but as the valve was buzzing and was 18 years old I figured I would just do it

As you have replaced the downstairs zone valve presumably the microswitch is OK, but the live signal isn't getting to the boiler. Disconnected or broken wire?

 

[ericmark]

Standard wiring is the programmer feeds the thermostats, which feeds the motorised valve, and the microswitch in the motorised valve feeds the boiler, so the replacing of the motorised valve makes sense.

But could just as easy be a broken wire.

 

[rich19754]

Just seems odd that it comes in when the upstairs is switched on - unless the brand new head is faulty (bought from screw fix yesterday)

 

[rich19754]

Standard wiring is the programmer feeds the thermostats, which feeds the motorised valve, and the microswitch in the motorised valve feeds the boiler, so the replacing of the motorised valve makes sense.

But could just as easy be a broken wire.

Yeah maybe so - will have another look. Just seems weird it comes on when upstairs is on

 

[CountryFan]

Just seems odd that it comes in when the upstairs is switched on - unless the brand new head is faulty (bought from screw fix yesterday)

Not really, if the downstairs zone valve is open and upstairs is also open and sending the switch live to the boiler, then the water will flow around the open downstairs port. As above, check the orange wire safely on the new head.

 

[terryplumb]

If the upstairs is switched on ,fires up the boiler,and downstairs switched off ( no call for heat from downstairs stat),do the downstairs rads still heat up ? If so ,the valve body of the downstairs valve must be physically stuck open.

 

[rich19754]

Not really, if the downstairs zone valve is open and upstairs is also open and sending the switch live to the boiler, then the water will flow around the open downstairs port. As above, check the orange wire safely on the new head.

Yeah got you - so how does the thermostat send the live to the boiler? The downstairs thermostat has a grey and brown wire connected and and an earth (unconnected) and a black wire (also unconnected). Upstairs thermostat just has grey and brown connected and earth unconnected but no black at all).

 

[terryplumb]

The motorised valve sends the voltage to the boiler to fire it up.
The motorised valve gets its voltage from the thermostat.

 

[rich19754]

If the upstairs is switched on ,fires up the boiler,and downstairs switched off ( no call for heat from downstairs stat),do the downstairs rads still heat up ? If so ,the valve body of the downstairs valve must be physically stuck open.

No the downstairs don’t come on unless the thermostat is cranked up

 

[rich19754]

The motorised valve sends the voltage to the boiler to fire it up.
The motorised valve gets its voltage from the thermostat.

Thanks - so it’s getting power to the valve to open the valve but then not sending it on to the boiler. So do I need to check/follow/test the orange wire between the valve and the boiler for any issues?

 

[CountryFan]

So do I need to check/follow/test the orange wire between the valve and the boiler for any issues?

Ideally yes, but just make sure it’s not loose first.

 

[terryplumb]

Yes ,you would need to do some voltage testing to establish if the orange wire at the wiring centre reads 230/240 volts . Are you competent to work safely on live circuitry ?