Wiring a Viessmann

[KevC1]

I'm swapping a Potterton for a heat only Viessmann. The Potterton has a switched live, and pump live.

Does anyone know if I can use the 1 and L terminal on the Viessmann as the switched live, and pump live? Or is the only way to have pump over run, is to use the flying lead supplied with the boiler?

Thanks for any replies.

 

[dhill]

The flying lead needs to be permanent live you ll need seperate wire for switch live. Last viessmann i fitted had nothing but problems make sure you really flush system out can be very sensitive to dirt in system

 

[JohnD]

you'd better say which model it is.

 

[mysteryman]

The mains lead on the Compact Heat Only is the permanent live from the fused spur. Terminal 1 on plug 96 is the switched live - remove the link but leave the capacitor in place. You should draw power from L & N on 96 for your external controls, so that your switched live power comes from the boiler. The pump live goes from plug 20.

 

[KevC1]

I think i'll wire it without the pump over run. It'll make life easier is I don't have to run a wire from boiler to the pump.

It's the vitodens 100 compact by the way.

 

[Tibbot]

I think i'll wire it without the pump over run. It'll make life easier is I don't have to run a wire from boiler to the pump.

Then it'll not work properly.

 

[mysteryman]

The current Compacts don't have to have the pump wired back to the boiler, but you lose the pump overrun and built in frost protection without it.

 

[matt1e]

The current Compacts don't have to have the pump wired back to the boiler, but you lose the pump overrun and built in frost protection without it.

No pump overrun to lose as non req
boiler will still have frost protection
system frost protection will have to be set by external controls as per norm

but I cant see what the problem off connecting the pump to the boiler is TBH if the cable is already at the boiler?
either use the flying lead supplied for socket 20 and connect the pump there 1= L / 2=N
or connect the pump live into 1 along with the boiler switched live as, as already stated this boiler doesnt have pump overrun

Matt

 

[holty]

confusing post. but here goes. on the terminal block you have from left to right. E,L,N THEN 1,L,N. the first E,L,N being the boiler perm live. then 1,L,N being for external controls. 1 being the switched live, but using the external L for a pump will only make the pump constantly run. thats why viessman supply a lead that plugs into block 20. the boiler needs a constant perm live. combined with a switched live, otherwise it will keep going in a purge cycle evertime its turned on. the boiler doesnt need pump overrun but its requirment it is covered by frost protection. e.g frost stat. p.s the boiler does have pump over run if the pump is fed by the lead of block 20.

 

[KevC1]

I don't really see a problem with it going through a purge every time it starts up, it only takes a few seconds.

I'm only asking these questions because i've only wired a few heat only boilers, and i like to try to make it as easy as possible for myself.

The existing boiler has a 5 core cable running to it, so i can use one of these as a switched live. I was trying to avoid running a cable from the boiler to the pump as it'll be a bit awkward.

 

[matt1e]

I don't really see a problem with it going through a purge every time it starts up, it only takes a few seconds.

I'm only asking these questions because i've only wired a few heat only boilers, and i like to try to make it as easy as possible for myself.

The existing boiler has a 5 core cable running to it, so i can use one of these as a switched live. I was trying to avoid running a cable from the boiler to the pump as it'll be a bit awkward.

then use the other core as a switch live to the pump and pick up pump neutral from the wiring centre

or as already stated common the pump with the boiler swqitched live as according to viessman pump overrun not req

 

[mysteryman]

You should not wire it so its boots up every time. It needs a permanent live. The built in frost protection needs the pump overrun connection.

 

[Agile]

With the luxury of a five core cable I dont see any problem providing an SWL and a boiler drive to the pump.

Its the two core and earth ones which need a little more ingenuity!

Tony

 

[KevC1]

I guess it's not ideal to have the boiler booting up from nothing every time there's a call for heat. I have done two this way with no problems.

I think I can manage to get the pump lead from the boiler back to the pump, then I can use one of the other cores as a switched live.

Thanks for all the help guys.

You need to use your brain a little more for a heat only than wiring a combi!!!!

 

[matt1e]

I think I can manage to get the pump lead from the boiler back to the pump, then I can use one of the other cores as a switched live.

Kev I don't think you're getting it,
you don't need to if you already have a five core there

View media item 28158
only downside is that the external controls will not be isolated via the boiler main switch as ideally they would be fed from the other L/N terminals but hey, are they ever!

Matt