Vaillant VSmart Thermostat - No heat demand

[Oh Danny Boy]

I have a Vaillant 418 boiler in a Y plan reconfiguration. I have just replaced the Honeywell thermostat and controller with a VSmart and VR66 system. Unfortunately I can't get the heating to turn on, but the hot water seems to run fine. I am getting a S30 No heat demand Controller status, but the thermostat is set higher than the room temperature. The 3 way valve moves to Water demand when requested, but when in Heating mode, I only get ~37V on the the white cable to CH1 Live. I also get the same reading on DHW ON Live, but I get ~240V on DHW OFF Live.

 

[CountryFan]

How did you remove the previous room thermostat? You’ve likely broken the circuit somewhere.

 

[Oh Danny Boy]

Hi Stuckinarut,

I removed the Honeywell thermostat wires as the VSmart has a wireless room thermostat. I then followed the instructions of the VR66 manual to install it. This includes the Honeywell cylinder thermostat and Drayton 3 way valve.

 

[CountryFan]

Which end? If the thermostat end, reconnect them and see if your heating fires up?

 

[RandomGrinch]

I removed the Honeywell thermostat wires as the VSmart has a wireless room thermostat. I then followed the instructions of the VR66 manual to install it. This includes the Honeywell cylinder thermostat and Drayton 3 way valve.

Your wiring appears correct to the VR66. But I'm not sure if the 24V RT link needs to be reinstated in the boiler, if all other external controls have been removed?

Has the eBus wiring been connected with the correct polarity, and was the VR66 turned back on before the boiler, as per the instructions?

I believe diagnosis code D.90 should show you the status of the eBus thermostat - whether it's connected or not, but I may be wrong.

 

[CountryFan]

Your wiring appears correct to the VR66. But I'm not sure if the 24V RT link needs to be reinstated in the boiler, if all other external controls have been removed?

You could be right there, I completely forgot about this. I don’t do much ebus stuff.

 

[Oh Danny Boy]

Which end? If the thermostat end, reconnect them and see if your heating fires up?

I disconnected them at the other end unfortunately, at the Honeywell wiring box, and then use that to rewire it for the VR66.

Your wiring appears correct to the VR66. But I'm not sure if the 24V RT link needs to be reinstated in the boiler, if all other external controls have been removed?

Has the eBus wiring been connected with the correct polarity, and was the VR66 turned back on before the boiler, as per the instructions?

I believe diagnosis code D.90 should show you the status of the eBus thermostat - whether it's connected or not, but I may be wrong.

Hi RandomGrinch,

Yeah I reconnected the jumper for the 24V RT, I also tried it without the jumper but didn't observe a change.

It has the correct polarity, but I didn't have it start before the boiler as they were connected on the same fused spur.

Yeah, D.90 shows that's connected.

It's very confusing because when I select hot water boost, the boiler fires up and works as it should.

 

[Harry Bloomfield]

It reads to me, as if the VR 66 might be faulty. Does the valve move at all? Is the 37 volt always around the same voltage, irrespective of call or no call?

What is the voltage, on the white L VR66 terminal, if the white is disconnected with a call for CH?

 

[CountryFan]

I disconnected them at the other end unfortunately, at the Honeywell wiring box, and then use that to rewire it for the VR66.

Can you show your wiring here?

 

[Oh Danny Boy]

It reads to me, as if the VR 66 might be faulty. Does the valve move at all? Is the 37 volt always around the same voltage, irrespective of call or no call?

What is the voltage, on the white L VR66 terminal, if the white is disconnected with a call for CH?

Yes I suspect it is faulty, but potentially only on the heating circuitry? It's very noisy, almost like a small rusty bearing spinning, I've never heard a circuit board be so noisy. I'm surprised that the led light shines green on it.

Yes the valve will move over to W when I request hot water. I actually got a lower voltage during one test, it was about 14V.

Unfortunately I have had to put the system back to the Honeywell controller as I have a baby who wasn't keen on the cold house...

Heating is working fine now, is it worth me testing some voltages to compare the outputs?

Can you show your wiring here?

Unfortunately I haven't taken a picture and I had to revert back. The wiring consisted of a E,L,N for the VR66 and a +/- for the EBus from the boiler. I also kept the pump wiring intact from the boiler.

 

[Harry Bloomfield]

Yes the valve will move over to W when I request hot water. I actually got a lower voltage during one test, it was about 14V.

So it must be moving the 3-port valve, from it's default position of HW? Just not far enough to trigger the heating?

I have a VR65 (I think), and it is absolutely silent.

Did you check this.....

What is the voltage, on the white L VR66 terminal, if the white is disconnected with a call for CH?

 

[RandomGrinch]

Yes I suspect it is faulty, but potentially only on the heating circuitry? It's very noisy, almost like a small rusty bearing spinning, I've never heard a circuit board be so noisy.

I agree with @Harry Bloomfield, a circuit board shouldn't be noisy.

Just for completeness, the 24V RT terminals should have a link in place, for eBus to function correctly.

But as you say...

Yeah, D.90 shows that's connected.

It's very confusing because when I select hot water boost, the boiler fires up and works as it should.

Proves communication is happening on the eBus.

The only thing I wasn't entirely sure about was...

Have you checked what the D.70 codes were?

 

[Oh Danny Boy]

So it must be moving the 3-port valve, from it's default position of HW? Just not far enough to trigger the heating?

I have a VR65 (I think), and it is absolutely silent.

Did you check this.....

It moved it over completely to Heating of the 3-port valve. I was getting the 37V during this period on both the white heating cable and the orange hot water cable. Apologies, I didn't take a measurement of it without the white cable connected.

I agree with @Harry Bloomfield, a circuit board shouldn't be noisy.

Just for completeness, the 24V RT terminals should have a link in place, for eBus to function correctly.

But as you say...

Proves communication is happening on the eBus.

The only thing I wasn't entirely sure about was...
View attachment 367510
Have you checked what the D.70 codes were?

I believe I had it set on 0, I think this was called Normal operation within the boiler GUI. I didn't ever see it go to mid position during this time so that would make sense.

 

[Harry Bloomfield]

I agree with @Harry Bloomfield, a circuit board shouldn't be noisy.

I'll make a guess at one of the relays being faulty, and chattering, hence the 37volts at the output.

I wasn't aware the Vaillant controls could use the mid-position of the valve, mine does not - it uses different boiler flow temperatures for heating, versus hot water. The only way it can do that, is by serving each, separately, at differing times. If there is a call for HW, then the CH goes off, until the HW is satisfied.