Thermostat not working

the_sphinx82

Hello, I had a thermostat for my combi boiler mounted and it wasn't working. I bought a new one of the same kind, rewired it and looks like it's working (the lights are on etc), but it doesn't "override" the boiler. The boiler is a Vaillant eco pro 24 and the thermostat a horstmann rf hrfs1. Could you please help? 

MikeJXE

What do you mean it doesn't override the boiler ?

A thermostat is just a switch that calls for heat or not, if you set it at 18 and the room is 19 it won't call for heat and the boiler won't fire up. 

If the boiler is running and you turn the thermostat down lower than what the room is the boiler should switch off. 

If thats not happening there is something wrong with thermostat or wiring 

the_sphinx82

Hi, with "override the boiler" I mean that wathever temperature I choose in the thermostat, the boiler will not go off. F.i. if my room temperature is 18 and I choose 5 in the thermostat, the boiler will continue heating no matter what.
The thermostat is new, and the wiring has been done following but the previous wiring and the diagram in the instructions 

bob_a_builder

There is often a 'link' wire in the boiler which need to be removed 

Example here
https://www.alswebpage.net/hive-with-installation-with-a-vaillant-ecotec-plus-824/

Can I see a small silver wire between 3 and 4 on your photo of the PCB ?

the_sphinx82

bob_a_builder said:

There is often a 'link' wire in the boiler which need to be removed 

Example here
https://www.alswebpage.net/hive-with-installation-with-a-vaillant-ecotec-plus-824/

Can I see a small silver wire between 3 and 4 on your photo of the PCB ?

Yes, I noticed it. Should be removed? And the withe and black wires are not connected to anything, don't know if that's an issue, too.

ThisIsWeird

the_sphinx82 said:

bob_a_builder said:

There is often a 'link' wire in the boiler which need to be removed 

Example here
https://www.alswebpage.net/hive-with-installation-with-a-vaillant-ecotec-plus-824/

Can I see a small silver wire between 3 and 4 on your photo of the PCB ?

Yes, I noticed it. Should be removed? And the withe and black wires are not connected to anything, don't know if that's an issue, too.

Yup - these are issues! I've zoomed in on these wires, and was going to ask you where they went - did they change to another colour? But you reckon they just 'end' there?! Lawdie.

Can you confirm?

I'd suggest - don't do anything until you understand fully what it is you are doing. In theory, yes, the link should be removed and the black and white wires go there instead - these go to 'com' and 'no' on your receiver, and effectively 'switch' together whenever the room stat calls for heat.

BUT, I presume your Horstmann DID work before it recently became faulty? If so, HOW the HECK?!

You say you swapped the wirers exactly as on the previous receiver? May I ask - why does this 'new' receiver look second-user? And, did you also replace the control unit - the HRFS1? Are you sure they are linked? If you only replaced the receiver, then it will require 'linking' to the existing stat.

But, I still don't understand how this ever worked...

Q - when you turn the 'stat up and down, does the receiver 'click'?

ThisIsWeird

Weirder and weirder.

Your boiler appears to be obtaining its mains power supply via the receiver. If you look at the receiver's wiring, there are two browns and blues. One of these pairs is likely to be the supply coming from the main isolating switch - I presume you have an isolating fused switch near the boiler? This seems to be supplying the receiver first, and then the boiler gets its L,N&E from the second pair of wires, via that large white cable coming in to the boiler. (I would normally expect the mains to be fed directly to the boiler, and then the receiver/controls to be fed from the boiler, but hey... No idea if this is 'bad', or 'how', but it seems 'wrong'.)

Check, please - can you confirm that, inside the plastic back box for the receiver, the two earths are absolutely connected together? If they are not, then your whole boiler is lacking an earth. Please check that now.

I can only conclude that the original Horstmann also did not control - 'override' as you call it - this boiler. I suspect that whoever wired it up was not fully aware of what they were doing.

I'd wait for a GasSafe on here to first confirm whether wiring the power supply to a boiler via a control unit is good practice. The next check would be - with everything isolated, and checked for 'dead' - to remove that link and see if the boiler then fails to come on for CH, regardless of what the Horstmann says.

Then it would be to confirm that the black and white wires are what they seem. You need to be 100% certain you are being guided correctly, have checked that these wires ARE what they appear to be, and are completely happy about what you are doing.

Q - did the OLD stat ever control that boiler?! 

the_sphinx82

ThisIsWeird said:

the_sphinx82 said:

bob_a_builder said:

There is often a 'link' wire in the boiler which need to be removed 

Example here
https://www.alswebpage.net/hive-with-installation-with-a-vaillant-ecotec-plus-824/

Can I see a small silver wire between 3 and 4 on your photo of the PCB ?

Yes, I noticed it. Should be removed? And the withe and black wires are not connected to anything, don't know if that's an issue, too.

Yup - these are issues! I've zoomed in on these wires, and was going to ask you where they went - did they change to another colour? But you reckon they just 'end' there?! Lawdie.

Can you confirm?

I'd suggest - don't do anything until you understand fully what it is you are doing. In theory, yes, the link should be removed and the black and white wires go there instead - these go to 'com' and 'no' on your receiver, and effectively 'switch' together whenever the room stat calls for heat.

BUT, I presume your Horstmann DID work before it recently became faulty? If so, HOW the HECK?!

You say you swapped the wirers exactly as on the previous receiver? May I ask - why does this 'new' receiver look second-user? And, did you also replace the control unit - the HRFS1? Are you sure they are linked? If you only replaced the receiver, then it will require 'linking' to the existing stat.

But, I still don't understand how this ever worked...

Q - when you turn the 'stat up and down, does the receiver 'click'?

Thanks for your answers. I have no idea if the thermostat was working fine before, I just moved and found it installed but with no remote. The receiver in the pics is the old one, and I rewired the new one the exact same. The control box and remote are connected, because when I select a  temperature in the remote, the control box switch on/off (green light and click).

I can confirm that the black and white are taped and end there. 

I will check the rest and let you know, thanks 🙏

The two Earth appear connected togheter. 

ThisIsWeird

Cool.

I would guess, then, that the previous controller did not have any effect on the boiler at all. The boiler was likely turned on and off manually, and room temps controlled using radiator TRVs.

Is there a programmer to time when the boiler comes on for CH?

How competent are you around electrics? Do you understand what's going on with these connections? Do you have a meter to confirm that the black and white wires ending inside the boiler do 'connect together' when the receiver is turned on by the 'stat? THIS WOULD BE TESTED ONLY AFTER YOU 100% CONFIRM THAT THE LARGE WHITE CABLE DOESN'T GO ANYWHERE ELSE EXCEPT BETWEEN THE RECEIVER AND BOILER, AND ALSO THAT THE B&W WIRES ONLY GO TO 'COM' AND 'NO', SO DO NOT HAVE A VOLTAGE IN THEM!

If you can do this, and provided you are 'happy' with your results, I would then personally consider it ok to connect the B&W wires to the link-removed terminals, 3&4. But YOU need to understand what you are doing.

(Wiring convention suggests that the 'com' in the receiver goes to '3', and 'no' to 4, but it'll work either way as the receiver is just a switch. But no other connections should be made to these - it's working as 'volt-free' contacts, which essentially means it isn't at mains voltage, but they do carry a voltage.)

markin

Did you get it working? Did the old one break, then someone bypassed it?