Yet Another Nest 3rd Gen Y Plan issue.

Joined
4 Oct 2021
Messages
9
Reaction score
0
Country
United Kingdom
Hey Guys,

Sorry I know there's been lots on here about nest and y plans. I thought I knew what I was doing but seems nothing I do works when it comes to boilers.

So, I have my third gen with 3 way valve control. My old unit was a c27 Honeywell control.

C27 standard type backplate. Neutral, live, hwoff(1) hwon(3) Chon(4)

On the nest I did the following - moved Chon(3) moved hwoff(4) moved hwon(6) bridged live to port 2 and 5. Added the neutral, live and earth terminals.

I thought great done, setup my nest flicked on hot water yeah it fired (oh no central heating is on) (turning up temp does fire the boiler and put heating on which I expect)

Initially the old thermostat was set to 0 in the hall way and nothing worked, I turned it to max and it kicked in so I thought oh I can blank that in the future (just leave at max for now) and allow nest thermostat to control heating and water.

To summarise I can't have hot water only without the heating and it's driving me nuts. - what does the "hot water control on/off" do in the nest app? I've turned it off.

Also to note there is the 3 way control valve is dodgey. But it was working fine on the honeywell before hand. I only say this because last year the heating was on with hot water and I gave the valve a whack and it sorted itself out.

Any help would be appreciated!

Thanks,
Chris
 
Sponsored Links
First of all I think you have your programmer confused. C27 is a Horstmann product not Honeywell. However from your description, and assuming that the 3-port valve is working correctly:

Check you have moved all of the wires correctly and that the conductor (and not the insulation) is securely fixed under the Heat link screw. Heat link terminals can be tricky even for those of us used to them.

C27 N = Nest N
C27 L = Nest L
C27 1 = Nest 4 (Hot Water Satisfied)
C27 3 = Nest 6 (Hot Water Call for Heat)
C27 4 = Nest 3 (Heating Call for Heat)

Link Nest L to the two common terminals 2 & 5

Existing room thermostat set to Maximum.
 
Last edited:
First of all I think you have your programmer confused. C27 is a Horstmann product not Honeywell. However from your description, and assuming that the 3-port valve is working correctly:

Check you have moved all of the wires correctly and that the conductor (and not the insulation) is securely fixed under the Heat link screw. Heat link terminals can be tricky even for those of us used to them.

C27 N = Nest N
C27 L = Nest L
C27 1 = Nest 4 (Hot Water Satisfied)
C27 3 = Nest 6 (Hot Water Call for Heat)
C27 4 = Nest 3 (Heating Call for Heat)

Link Nest L to the two common terminals 2 & 5

Existing room thermostat set to Maximum.

Thanks! I'll double check wiring when I get home this evening. I know it sounds stupid but the screw on the nest pinches the wire from a bottom up position so just make sure it get pinched in that gap?

Also yeah I thought it was Horstman when I googled it. But the one I have definitely saying Honeywell C27 but it looks pretty much identical to Horstman so not too sure what's going on there.

Looks like I have my cabling correct though!

Thanks,
Chris
 
First of all I think you have your programmer confused. C27 is a Horstmann product not Honeywell. However from your description, and assuming that the 3-port valve is working correctly:

Check you have moved all of the wires correctly and that the conductor (and not the insulation) is securely fixed under the Heat link screw. Heat link terminals can be tricky even for those of us used to them.

C27 N = Nest N
C27 L = Nest L
C27 1 = Nest 4 (Hot Water Satisfied)
C27 3 = Nest 6 (Hot Water Call for Heat)
C27 4 = Nest 3 (Heating Call for Heat)

Link Nest L to the two common terminals 2 & 5

Existing room thermostat set to Maximum.
On further looking I've just noticed turning the thermostat up doesn't kick the heating in. Boosting water only turns heating on.....
 
Sponsored Links
Might you have an underlying issue with the 3 port? Was it working correctly on the C27?
 
Might you have an underlying issue with the 3 port? Was it working correctly on the C27?
It definitely was working with the C27. However.... About a year ago I did have an issue with it and slapping it seemed to cure it.
 
If it wa ps working previously then it’s likely a wiring issue, but if you’re certain the wiring is correct then it’s likely the valve.
 
Added all the pictures below if someone can confirm. My link cables are brown.

Cheers,
Chris
 

Attachments

  • PXL_20211004_122100336.jpg
    PXL_20211004_122100336.jpg
    261.4 KB · Views: 97
  • PXL_20211004_121924035.jpg
    PXL_20211004_121924035.jpg
    170.3 KB · Views: 91
  • PXL_20211002_143300834.jpg
    PXL_20211002_143300834.jpg
    176.3 KB · Views: 106
Damn.

Think I have wired wrong due to it being gravity fed which I assumed was Y plan.

Does below look legit? The only bit that doesn't look right is link 3-4 as well. When CH is on HW needs to be on too.

You can do it without a relay if you do the wiring to the nest slightly different.
Connect L and N as normal
Link L to 2 and 6 (instead of 5)
Connect pump to 3
Connect boiler to 5 (instead of 6)
Then also link 3 to 4
This way when you just set heating it will fire the boiler up as well as the pump.

Read more: https://www.diynot.com/diy/threads/...ot-water-pumped-heating.493177/#ixzz78KbbWyc7
 
You dont have a gravity HW system you have a Y plan fully pumped sytem, Gravity is something completely different
 
I do have Gravity. I have a water tank in the loft which refills the tank in the airoom cupboard. So it must be gravity?

I still have the 3 way valve. So I'm quite unsure what y plan is now actually.
 
Last edited:
I do have Gravity. I have a water tank in the loft which refills the tank in the airoom cupboard. So it must be gravity?

I still have the 3 way valve. So I'm quite unsure what y plan is now actually.
Yes that part is gravity fed, but if you have a circulator (aka a pump) then it’s fully pumped.
 
I do have Gravity. I have a water tank in the loft which refills the tank in the airoom cupboard. So it must be gravity?

I still have the 3 way valve. So I'm quite unsure what y plan is now actually.
You dont have Gravity, you have open vent, gravity is something completely different
 
I do have Gravity. I have a water tank in the loft which refills the tank in the airoom cupboard. So it must be gravity?

I still have the 3 way valve. So I'm quite unsure what y plan is now actually.
The hot water to the taps is by gravity, that's the secondary circuit. The primary (closed) circuit through the coil is pumped hot water from the boiler.
Y-plan has a mid-position 3-port valve, as you've said. When HW is called, the valve closes to the rads and sends hot water to the cylinder coil. When CH is called, it closes to the cylinder and sends hot water to the rads. When both HW and CH are called the valve moves to mid-position so both cylinder and rads get hot water. That's if everything is wired up correctly.
 
Okay. If that's the case then why would heating come on when I press water. And nothing happens when I turn heating on?

The C27 on the back of it told me which wires went where so I just followed the right instructions.
 

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.


Are you a trade or supplier? You can create your listing free at DIYnot Local

 
Sponsored Links
Back
Top