question about wiring for a Viessmann Vitodens 100-W

[Por968t]

Got a customer called me out to a problem with a boiler (above boiler) It was installed before christmas by a gas safe plumber, and he from what I understand copied the wiring from the old boiler assuming it would work, it doesn't. He said to them that he would send over an electrician to sort it, and he didn't, and now won't answer the phone.

Its an oil fired boiled, with a DHW tank with immersion heater, its got a stat on the cylinder, and the existing room stat and controller for CH and HW

He didn't touch the room stat or the controller wiring.

The issue with the boiler is, there is no hot water (unless using the immersion heater)

when I opened the junction box the wiring to the new 3 way valve was all loose, I reconnected it where it was and nothing, the CH works from the controller in the sitting room, but when you try and put the HW on, nothing happens.

The new pump is wired directly into the junction box, there is a LNE coming from the boiler to the JB, and a SL, but thats it.

The wiring looks to be a standard Y plan wiring, apart from the L for the pump is wired into terminal 4 (the Y plan wiring shows the pump live wired into PL on the boiler

Not only does the pump not fire up when the DHW is selected, the tap symbol doesn't appear on the boiler display, its like the boiler has no idea its being asked to fire up for the DHW

TIA for any help

 

[stem]

The motorised valve when unpowered sits at rest in the hot water position, so when HW is selected on at the programmer, a live is supplied to the cylinder thermostat and if that if calling for heat will start the boiler & pump. Which isn't happening.

The motorised valve has a grey wire, this wire is energised when the hot water is not required and the motorised valve winds fully across to close the hot water port. So it could be that this wire is being made live when it shouldn't be. I have seen installations where the wiring to the connections at the cylinder thermostat or programmer have been transposed so that the controls for the hot water work in reverse. Meaning when hot water is required it actually closes the hot water port instead of leaving it open.

Below is a Y Plan wiring diagram I would start by checking that only the Programmer HW 'off ' and Cylinder thermostat 'satisfied' wiring terminals are connected to the motorised valves grey wire.

If the cylinder thermostat wiring is transposed (i.e. 1 &2 in the example above) then turning the cylinder thermostat setting down below the point where it 'clicks' might start the hot water heating.

You've not mentioned if the cylinder thermostat was changed or not, or if it was working properly to start with.

 

[Por968t]

The motorised valve when unpowered sits at rest in the hot water position, so when HW is selected on at the programmer, a live is supplied to the cylinder thermostat and if that if calling for heat will start the boiler & pump. Which isn't happening.

The motorised valve has a grey wire, this wire is energised when the hot water is not required and the motorised valve winds fully across to close the hot water port. So it could be that this wire is being made live when it shouldn't be. I have seen installations where the wiring to the connections at the cylinder thermostat or programmer have been transposed so that the controls for the hot water work in reverse. Meaning when hot water is required it actually closes the hot water port instead of leaving it open.

Below is a Y Plan wiring diagram I would start by checking that only the Programmer HW 'off ' and Cylinder thermostat 'satisfied' wiring terminals are connected to the motorised valves grey wire.

View attachment 225655

If the cylinder thermostat wiring is transposed (i.e. 1 &2 in the example above) then turning the cylinder thermostat setting down below the point where it 'clicks' might start the hot water heating.

You've not mentioned if the cylinder thermostat was changed or not, or if it was working properly to start with.

the cylinder and stat were not changed, it had a new pump, valve and boiler, everything else is existing...

the one thing I have read is that these boilers have a pump wiring connector directly to the PCB on the boiler, this is not fitted on this one, also the wiring diagram for the boiler wiring shows a jumper wire between 1 and L for some instances?

 

[Terrywookfit]

Vitodens 100 is a gas boiler not oil.

 

[ianmcd]

As @Terrywookfit says if it is an oil boiler it isnt a 100-W

 

[Por968t]

sorry your right, its gas, was confusing the one we wired in the previous day

 

[ianmcd]

sorry your right, its gas, was confusing the one we wired in the previous day

Not much difference

 

[stem]

With a Y-Plan system, the controls package provides a common live supply to the boiler / pump that simply tell them to 'go'. This is the same live connection irrespective of whether it's the radiators or hot water that require heat. The motorised valve will then select where the water goes. Heating, hot water, or both.

when the DHW is selected, the tap symbol doesn't appear on the boiler display

Because a Y-Plan provides one single live supply to the boiler for both heating and hot water it's not possible for the boiler to differentiate which of them is calling for heat. I have to say I'm not familiar with this boiler (but have worked on a few Y-Plans ) To me a tap symbol sounds more akin to a combi boiler.

 

[DavidLewis]

If it's a 4-pipe system boiler, its internal diverter valve should be in operation, and not the external Y-plan one. If it's plumbed as a 2-pipe boiler, I think (but someone qualified should verify this) that the internal diverter's electrical connector should be unplugged, and the external Y-plan valve wired in.

(I know the OP mentions a new pump, which would imply it's not a system boiler, but then he also mentions a Y-plan valve that is no longer wired in...)

 

[stem]

he also mentions a Y-plan valve that is no longer wired in...

I didn't understand it like that. The OP said the wiring was originally "loose" but also that...

it had a new pump, valve and boiler,

Why would you install a new valve and not wire it in? Without power it would just sit permanently in the hot water only position and the central heating would never work....perhaps that is the case and the valve is in the wrong way around so only the heating is working instead.

All very odd. Maybe we are only getting half the story.

 

[Razor900]

If its a 4 pipe boiler it needs the veissmann cylinder sensor to tell the boiler when it's supposed to be reheating the hot water