Changing from W Plan to Y Plan Heating

[Arctor]

Hi,

I bought a Nest unit recently having checked for compatibility with the Nest survey on their site. Unfortunately, their survey did not take into account W Plan heating which is not compatible but which they indicated would be okay. Having looked into the situation for the last couple of days (and discovered that there is some blackening/charring beginning to occur inside the case of my ancient Randall 3022 controller so it definitely must go) I think the best solution is to swap the system to Y Plan and install the nest.

I have ordered a straight swap Honeywell mid position, 3 port valve and a Salus Wiring Centre. The valve "should" be straightforward to change and I have spent some considerable time studying up on the wiring (the way I found this great place) and feel capable of rewiring the system into the wiring centre.

The issue I have is the wiring in the boiler. I have an old British Gas RD1 boiler and (surprise surprise) it doesn't follow the modern standard wiring diagrams. The pump is not wired into the boiler direct but is wired into the controller in the upstairs airing cupboard. This is as per the instructions in the boiler manual so I am assuming I can just swap this over to being wired into the wiring centre in the Y Plan setup (again as per the manual). The thing that is vexing me is the switched live wiring.

Currently the set up seems to be that the live feed comes down to the boiler from the controller unit and is wired into L N E terminals then a permanent connection goes from the live terminal to the EC1 terminal which is supposed to be used for the switched live. This must work due to the mains supply itself being used as the switch via the wiring in the current control unit. This is not to modern wiring diagrams or the y plan set up in the boiler manual but can I just swap this over as is or should I change the wiring putting a separate switched live in from the wiring centre? And if I do that is it okay to leave the mains supply to the boiler coming from the wiring centre?

Thanks for any help and sorry for the mammoth post but I am trying to keep everything straight in my tiny brain as much as anything else!

Edit: N.B. My tiny brain also decided to put the wrong title on my first post here. D'oh - it is Y Plan that I am trying to convert to. Clearly I have plan fug...... fixed - Mod

 

[D_Hailsham]

Some things you say don't add up.

What make/model motorized valve do you have at the moment?

 

[Arctor]

thanks for the reply.

The fitted valve is a Honeywell 4044C diverter valve.

 

[MrTherm]

The standard Y plan uses a Honeywell V4073A (3 position) valve and not a 4044C (2 position) valve you say is currently fitted and which is used in the sundial W plan (fully pumped single zone at any one time) - it has three wires not five like the V4073A.

 

[Arctor]

Yep - it is W Plan that the system is currently set up as. I want to change it to Y Plan - I have a 4073A being delivered tomorrow.

 

[ianmcd]

you will need to wire a HW off into your new system you will not have that at present

 

[D_Hailsham]

The pump is not wired into the boiler direct but is wired into the controller in the upstairs airing cupboard. This is as per the instructions in the boiler manual

Thanks for valve info, which saved asking other questions.

Where, in the boiler manual, did you read that the pump should be connected to the controllerl? The boiler has two terminals marked PL and PN, i.e Pump Live and Pump Neutral, to which the pump should be connected. (Page 21 of installation manual)

I think it might be best to ignore the current wiring and start again.

Edit: The note at the bottom of page 21 re gravity systems does not apply to you as you have a fully pumped system, not a gravity one.

 

[Arctor]

Hi again and thanks for the replies. I'm afraid I was rushing due to a minor domestic emergency last week and confused myself when looking inside the boiler as it didn't match my expectations. Unfortunately, it has also meant I haven't had time to spend on this so am starting again this weekend. I understood why the boiler is wired as it is when I checked the correct W plan wiring diagram on Monday - there is no permanent live wired into the boiler in the W plan so both the permanent and switched live have been connected (in a rush on Sunday I had looked at a diagram via Google that showed a permanent live wired in - not W plan - and this is what really confused me).

The pump being wired into the wiring centre is on p.23 of the manual in the wiring diagram for a mid position valve set up (or Y plan as I understand it).

It is this that originally prompted me to sign up as I don't like changing things that work unless there is a significant benefit and the way the boiler is wired has been fine for 12 years. Without the pump being wired into the boiler direct I could see no benefit in altering the wiring so there are separate permanent and switched live wires and I could just keep the current setup adapted to the Y plan. So is this assumption correct or is there another benefit I am missing? Or is the diagram on p.23 wrong and and I should wire the pump to the boiler?

 

[MrTherm]

For reference and to assist with replies for explaining wiring etc.

Install manual for British Gas RD1 gas boiler.

http://idealboilers.com/installer/wp-content/uploads/sites/2/2013/08/157022.pdf

regards

 

[Arctor]

Thank you! I should have done that myself, sorry.

 

[D_Hailsham]

is the diagram on p.23 wrong and and I should wire the pump to the boiler?

The diagrams for mid-position (Y Plan) and zone valves (S Plan) do show the pump connected to the junction box and not to the boilers PL and PN terminals. I can't explain this; it doesn't make sense.

Why have pump terminals on the boiler and then not use them? (They tell you not to use them for pumped heating/gravity hot water systems, e.g. C Plan systems, so logic says you must use them for fully pumped systems.) Maybe they just copied the Y and S plan diagrams from another boiler, without modifying them for pump overrun.

May be a GSR could advise what to do.

 

[Arctor]

Just to say thanks for trying to help. I ended up wiring the system as per the boiler manual. I agree it seems daft as there are pump terminals on the boiler and it seems the only reason to add the permanent live feed would be to make use of these but as a DIYer I thought it best to follow the manual in the absence of further, more professional advice.

The system has been up and working for nearly a week now and the boss is moving me on to planning a revamp of the bathroom.......