Not getting pump over run on y plan

[Rizme]

Morning

Fitted a Vaillant 637 on a Y Plan, It has santon premier plus unvented tank and a new Honeywell ST95 a two channel programmer. Everything seems to work correctly as in when the demand for hot water or heating is requested the boiler fires. But as soon as if you turn it off from the clock or room stat the boiler switches off as in the digital display goes off and the boiler shuts no pump over run.

What am I missing here. The tank is upstairs and the boiler down stairs checked all my wiring everything seems to be correct as per the honeywell diagram which comes along with the clock.

Any help much appreciated.

 

[galaxy_plumbing]

maybe you have missed something silly where was it wired into?

 

[Rizme]

maybe you have missed something silly where was it wired into?

It was wired into a Honeywell clock the one below.

 

[GasmanxxxR1]

Sounds like you have no perment live to the boiler, its working on a switch live

 

[GasmanxxxR1]

Are you using 5 core flex?

 

[mountainman]

Pump overrun comes from the boiler which itself needs a permanent live.
Check the wiring diagram in the MI's.

 

[tamz]

You also need a bypass as your unvented cylinder should still have the 2 port valve fitted.

 

[Rizme]

You also need a bypass as your unvented cylinder should still have the 2 port valve fitted.

By pass is there as in a gate valve, I have just replaced the boiler and the clock and had to re-wire again.
There is no space for two port even if I have to do it.

 

[Rizme]

Are you using 5 core flex?

Well I had to make use of existing cables as the previous installer has fitted the the switch for the boiler and the clock behind the washing machine under the work top. Not much of a slag on the cable. ( don't you just love such installation NOT),

 

[GasmanxxxR1]

Have you got 5 wires at the boiler? L N E SL PL

 

[Rizme]

Have you got 5 wires at the boiler? L N E SL PL

the boiler has only 3 terminal L N E, although I have 5 core cable coming into it, the br wire is connected to the orange wire on the zone valve which act as a switch live , if I connect the Br on live it will stay on without any demand.

 

[tamz]

637 is a system boiler so you'll need 4 wires. LNE onto the green block on the right and switch live onto RT on the purple block next to the green.
Remove the link from the white 24v block to the left.

You still need a 2 port valve fitting on the hw side.

 

[Rizme]

637 is a system boiler so you'll need 4 wires. LNE onto the green block on the right and switch live onto RT on the purple block next to the green.
Remove the link from the white 24v block to the left.

You still need a 2 port valve fitting on the hw side.

If there is no provision for 2 port to be fitted what other alternate can one go.

I did the above option by connecting the SL on the RT terminal and the L wire from the boiler on the L in the terminal box and the SL on the orange of Zone valve. The boiler was on without any demand.

 

[GasmanxxxR1]

You need to remove the link, i think

Can the two port gon on the hw return anywhere

 

[tamz]

You need to take the 24v link out. White plug with 24v on it on the left side of the board.
As said if you are stuck put the 2 port on the hw return or fit it next to the cylinder.

 

[Rizme]

Many thanks for all your help. It was the 24 v link on the boiler which I forgot to remove. All good now.

 

[GasmanxxxR1]

Have you been able to rectify the need for a two port valve?