Honeywell F&E using Nest

jaber · 7 Apr 2019

Hi all

I have installed a few radio thermostats into combi boilers in the past. Simple install, simply a glorified switch. However, my new house appears to have an old heating system approx 20 years old.

I believe it may be a an F&E? It has a boiler in adjoining garage, copper tank and water tank(s) in the loft. The thermostat is a Honeywell, control box by copper tank and remote thermostat on the wall downstairs. pictures attached.

On closer inspection, it appears both have a mains supply and will fry my nest. I am keen to learn and do the install myself. Do I need a transformer for the Nest control box and remote unit? Is the thermostat on the mains rig or lighting rig?

Regards... J

jaber · 7 Apr 2019

+Boilet

ianmcd · 7 Apr 2019

you have an open vent Y plan system there should be a wiring diagram for Yplan with you nest if not google it there are loads open vent (what you call F&E) and sealed system are wired exactly the same so just look for Y plan

jaber · 7 Apr 2019

Thx Ian - knowing the correct system name is a good start

MeldrewsMate · 7 Apr 2019

The Nest receiver is designed to switch 240vac, and is powered from 240vac. Its T1 and T2 connections supply 12vdc to the user display, allowing the old wiring to the old thermostat to be re-used, and avoiding the need for the Nest optional power supply (unless you want to use the optional desk stand).
The biggest bugbear with the Nest IMO is the small size of the terminals on the receiver, getting two 0.5mm2 wires into one terminal is a bit of a challenge!

jaber · 7 Apr 2019

Ah ok, thanks for the heads up on the power to the display. I did see any feed from the old thermostat, is it possible it’s radio? Only, look a bit old to me.

The Nest is up and running, love it.

ianmcd · 7 Apr 2019

MeldrewsMate said:
getting two 0.5mm2 wires into one terminal is a bit of a challenge!

you should not be using 0.5mm2 on a heating system, the minimum is 0.75mm2

jaber · 7 Apr 2019

How can I tell if the hot water is working? Unlike the CH, it doesn’t appear to make a noise when switched on.

Or, have I wired it incorrect... even though I triple checked? Thx

MeldrewsMate · 7 Apr 2019

ianmcd said:
you should not be using 0.5mm2 on a heating system, the minimum is 0.75mm2

Evenmore of a challenge with 0.75mm2 then!

I disagree, a 0.5mm2 flexible cord is very capable of carrying the load expected of a heating system, and suitably protected with a 3A BS1362 fuse...according to my old BS7671 (17th edition!).

bernardgreen · 8 Apr 2019

MeldrewsMate said:
a 0.5mm2 flexible cord is very capable of carrying the load expected of a heating system, and suitably protected with a 3A BS1362 fuse

That is fine as long as the fuse is 3 amp and not 13 amp ( or a bent paper clip ) 0.5mm² cable could get hot before a 13 amp fuse melts on overload current.

EFLImpudence · 8 Apr 2019

What is it, in such a heating system, that can cause such an overload?

ianmcd · 8 Apr 2019

EFLImpudence said:
What is it, in such a heating system, that can cause such an overload?

Its the BS factor from those that have no clue

MeldrewsMate · 8 Apr 2019

There are tables in the British (not oooo-row-pee-an) Standard that indicate the disconnection time (blowing the fuse time) for a BS1362 fuse. It can be several hours at the rated current (3A, 13A, etc). Some may cruelly joke that the wrong fuse rating in a 506 years old cottage with a thatched roof could solve a nagging problem....not me though!

bernardgreen · 9 Apr 2019

EFLImpudence said:
What is it, in such a heating system, that can cause such an overload?

A fault

ianmcd said:
Its the BS factor from those that have no clue

So is it BS from the manufacturers who state that the supply to boiler and controls must ( should ) be fused at 3 amps ?

EFLImpudence · 9 Apr 2019

bernardgreen said:
A fault

Somewhat vague??? An example?

So is it BS from the manufacturers who state that the supply to boiler and controls must ( should ) be fused at 3 amps ?

Probably, yes - like the same for extractor fans. It's just what they write.

If their product requires fusing, they should fit integral fuses. Oh, they do.

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