Honeywell Evohome with Vaillant boiler

[MikeJJJ]

Can anyone help please? I am a reasonably competent DIYer and have a small project I think I could handle.
My central heating controller has failed and I'd like to fit a replacement. The current system is a Honeywell Smartfit low voltage controller which drives a Vaillant Ecoflex Plus boiler. I am minded to go smart with a Honeywell Evohome controller. The zone valves are being replaced next week with 240v ones and while the system is drained down I will replace some of the TRVs to take the Honeywell heads.

The system is S Plan and I plan to use BDR1 relays and a HW pack to control the MVs.

My question is: How do I get the hot water demand to the boiler? Currently the Smartfit system is connected with a 4 core cable (3 + earth) which carries 240v ELN and a BLACK wire which connects the SL Smartfit terminal to connector 4 on the boiler. Logically I'd guess that the ORANGE wires from the MVs should go to terminal 4 on the boiler. (Vaillant unhelpfully only use numbers) Is this correct or will I need to use another BDR1 relay to switch the boiler?

 

[ShaunCorbs]

best bet is to get a heating engy in to do the wiring for you as you cant remove the cover to the boiler unless your gas safe

and its not cheap kit if you install it wrong

 

[MikeJJJ]

Shaun, thanks for your response. I take your point about GS but I wouldn't need to go into the boiler. The existing terminal block in Smartfit is already connected to terminal 4 in the boiler with the BLACK wire as described - all I would have to do is connect the ORANGE wires to this terminal (or replacement connector block in actual fact) if this is correct.
PS the boiler is in the garage and the controller is in an upstairs airing cupboard. I have a GS heating engineer coming next week to service the boiler and drain, change the zone valves and chemically flush and refill the system but he won't touch the electrics.

 

[ShaunCorbs]

depends but without looking at it cant be sure

but best bet would be if you want to go down the evo home route is to remove all of the vaillant controls and go full evo home

 

[MikeJJJ]

Sorry Shaun, I don't seem to be explain myself very well:whatchutalkingabout. Thanks for your patience.

It doesn't use Vaillant controls - it had a Honeywell Smartfit system which used to control the zone valves etc and tell the boiler to switch on via the 4 core cable (which incidentally also supplied mains to the controller). The Smartfit programmer has failed and I cannot get a replacement as they are discontinued so I looked for an alternative and was recommended the Evohome as an easy fit option, It seems a good solution and straightforward but I am not absolutely certain about the connection to the boiler.

In the Vaillant manual terminal 4 is for an external timer/thermostat. I'm assuming that that is what the Evohome appears to the boiler as. In which case the MV switch is equivalent to a timer/thermostat switch. ie the Evohome tells the MV to open and the switch returns the 'open' condition on the ORANGE wire. But is it safe to assume this and connect this to the boiler? If it is then great but I don't want to break the boiler by giving a mains voltage it doesn't expect.
Actually I think the simple question is: is the Vaillant terminal 4 the PL terminal? In which case connecting the SL from the controller to the PL seems logically correct?
My secondary question would be: if the above isn't the solution then what is?

 

[ShaunCorbs]

sorry i get where your coming from now

right depends on how its been wired as your pump might be wired to the boiler (pump overrun)

normally have mains LNE at the boiler via a fused spur

the run a 4 core to airing cupboard, for your s/l (port 4) and your pump LNE



normally how s plans are done (that diagram doesnt show pump overrun)

 

[MikeJJJ]

Thanks Shaun
What you describe is right - except I cant view the picture for some reason. The pump is actually within the boiler so the LNE is only for the controller and presumably the SL back to the boiler. I think I've got it now and should be able to get on with it.
I just found that a Honeywell Evohome accredited engineer lives just around the corner so maybe I'll see if he'll sell me an hour of his time before I switch it on!

 

[MikeJJJ]

Thanks Shaun
What you describe is right - except I cant view the picture for some reason. The pump is actually within the boiler so the LNE is only for the controller and presumably the SL back to the boiler. I think I've got it now and should be able to get on with it.
I just found that a Honeywell Evohome accredited engineer lives just around the corner so maybe I'll see if he'll sell me an hour of his time before I switch it on!

 

[ShaunCorbs]

Thanks Shaun
What you describe is right - except I cant view the picture for some reason. The pump is actually within the boiler so the LNE is only for the controller and presumably the SL back to the boiler. I think I've got it now and should be able to get on with it.
I just found that a Honeywell Evohome accredited engineer lives just around the corner so maybe I'll see if he'll sell me an hour of his time before I switch it on!

or maybe ask him for a quote to install it, but where here if you need us