Vaillant boiler controls

[Mattg4321]

Does anyone here have any experience with Vaillant boiler controls, specifically VRC720?

 

My parents have just had a new boiler fitted. Ecotec Pure 618 and nobody can seem to get the VRC720 to switch the boiler on when it’s calling for heating. Boiler showing status code s30 - thermostat is blocking heating mode. 
 

All connected together with Bus cables as per instructions and everything works as it should including DHW valve opening and boiler firing. It’s wired to a VR66/2 - dial setting 1 for monozone.  Also has outside temp sensor and set up as hot water priority. 
 

Guessing it may be something to do with outside temp being too high, but changed that setting to 35 degrees c, so it shouldn’t be that stopping thermostat from sending signal to open valve and fire boiler (neither of which are happening)

 

Should be going there again to meet fitter on Monday and probably call technical support, but would like to be armed with suggestions! Cheers

[Nickfromwales]

Have you tried lowering the DHW set temp to its lowest setting in case DHW priority is blocking it? Is the boiler cycling back>forth the cylinder?

 

6 series is a system boiler iirc?

[Mattg4321]

10 minutes ago, Nickfromwales said:

Have you tried lowering the DHW set temp to its lowest setting in case DHW priority is blocking it? Is the boiler cycling back>forth the cylinder?

 

6 series is a system boiler iirc?

Tried turning off the DHW and also when the DHW is up to temp, still doesn’t turn on the central heating. No radiator symbol on the boiler, valve doesn’t open and S30 status. 
 

Yes, it’s a system boiler. Thanks 

[Nickfromwales]

Says to link t3 and t4 at the boiler to ‘reset’.

 

Best to try and default it all, but likely a call to tech support will sort it while you’re there.

[JamesPa]

2 hours ago, Mattg4321 said:

s30 - thermostat is blocking heating mode. 

Surely that is the key.  The Vaillant manual that O looked at says 'Room thermostat is blocking heating mode'.  Have you got a room thermostat and if so is it working.  If you haven't got a room thermostat (there is no need with the VRC720 since it has an internal temperature sensor) have you/your installer told the boiler to ignore the demand for heat signal and/or that there is no room thermostat.

 

As an aside the outdoor sensor is presumably so it can do weather compensation, has the compensation curve been set?

 

Edited July 26 by JamesPa

[Mattg4321]

2 minutes ago, JamesPa said:

Surely that is the key.  The Vaillant manual that O looked at says 'Room thermostat is blocking heating mode'.  Have you got a room thermostat and if so is it working.  If you haven't got a room thermostat (there is no need with the VRC720 since it has an internal temperature sensor) have you/your installer told the boiler to ignore the demand for heat signal and/or that there is no room thermostat.

 

As an aside the outdoor sensor is presumably so it can do weather compensation, has the compensation curve been set?

 

No room stat other than the VRC720, which is talking to boiler as all information from boiler available on VRC720 and hot water controlled from VRC720 turns boiler on as expected. 
 

Maybe there’s some setting somewhere that means the boiler thinks there another room stat - which there isn’t.

[JohnMo]

2 hours ago, Mattg4321 said:

Boiler showing status code s30 - thermostat is blocking heating mode

 

6 minutes ago, Mattg4321 said:

No room stat other than the VRC720

Have you not answered your own question - if the controller thinks there is a thermostat it is seeing open connection somewhere. So there must be connection for external thermostat? To get the system to work those terminals need to see continuity, so need a short across the two terminals. Or system needs to be configured within the controller not to look for an external thermostat.

 

 

[SimonD]

34 minutes ago, JamesPa said:

has the compensation curve been set?

 

Yes, check this first. I don't work on enough Vaillants and their controls to know this off the top of my head, but the last time I saw a problem like this was the compensation curve set too low and the room stat/controller apparently still calling for heat but boiler only running at low flow temp so never reaching target - this was in the middle of winter with new house owners scratching their heads. A quick change to the curve and it all worked okay - but Vaillant controls are so dense and inaccessible, it doesn't help at all.

[Mattg4321]

2 minutes ago, SimonD said:

 

Yes, check this first. I don't work on enough Vaillants and their controls to know this off the top of my head, but the last time I saw a problem like this was the compensation curve set too low and the room stat/controller apparently still calling for heat but boiler only running at low flow temp so never reaching target - this was in the middle of winter with new house owners scratching their heads. A quick change to the curve and it all worked okay - but Vaillant controls are so dense and inaccessible, it doesn't help at all.

Weather compensation curve set to highest possible setting!

[Mattg4321]

27 minutes ago, JohnMo said:

 

Have you not answered your own question - if the controller thinks there is a thermostat it is seeing open connection somewhere. So there must be connection for external thermostat? To get the system to work those terminals need to see continuity, so need a short across the two terminals. Or system needs to be configured within the controller not to look for an external thermostat.

 

 

There is a connection for an external stat, but it’s linked out already as per the wiring diagram!

 

 

[Nickfromwales]

11 minutes ago, Mattg4321 said:

There is a connection for an external stat, but it’s linked out already as per the wiring diagram!

 

 

Have you tried it with the link out? 

[JamesPa]

1 hour ago, Mattg4321 said:

No room stat other than the VRC720, which is talking to boiler as all information from boiler available on VRC720 and hot water controlled from VRC720 turns boiler on as expected. 

Ok so (a) what @Nickfromwales and @JohnMo   said about the thermostat and (b) how do you know there is a call for heat (you say there is but how do you know?).  What's the current oat and what is the target room temp on the VRC720?

Edited July 26 by JamesPa

[Mattg4321]

53 minutes ago, JamesPa said:

Ok so (a) what @Nickfromwales and @JohnMo   said about the thermostat and (b) how do you know there is a call for heat (you say there is but how do you know?).  What's the current oat and what is the target room temp on the VRC720?

Outside air temp was 22.5 earlier. 
Desired (target) temp was 30

inside temp was 23.5

outside air switch off limit changed to 35

Heating set to manual on

 

not sure what else I can do!

[Mattg4321]

1 hour ago, Nickfromwales said:

Have you tried it with the link out? 

No, as that’s not what the manual says. 
 

I’ve just had another look and reminded myself of the relevant settings in the manual. I’m fairly sure they are all set to the below, but I will check them tomorrow. Perhaps the zone isn’t set to activated or something. 
 

Not sure why Vaillant make things overly complicated,  but also their instructions are not the most intuitive