DIYnot
Local | Network
   DIYnot > Forums
Local | Network
DIYnot Network Local DIYnot Network Local  
  Forum IndexForum Index     RulesRules    HelpHelp     Join FREERegister Free     About CookiesCookies     SearchSearch     LoginLogin 

Wiring new cylinder thermostat


 
Post new topic   Reply to topic    DIYnot.com Forum Index > Plumbing and Central Heating
Search this topic :: View previous topic :: View next topic  
Author Message
StrikeThree

from United Kingdom

Joined: 20 Nov 2011
Posts: 4
Location: Middlesex,
United Kingdom

PostPosted: Sun Nov 20, 2011 12:58 am Reply with quote

I am replacing a cylinder thermostat in a central heating system and would appreciate any wiring advice.
The old thermostat is a Satchwell. It is very old, settings in Fahrenheit. It has three connections. One wire is yellow and black sleeved and is connected to the metal thermostat housing (so must be earth). The other two wires are coloured red and blue. Their terminals both go to 240V (wrt earth) when heating is on, both are at 0V when heating off.
The new thermostat is a Horstmann HCT2. It has three terminals, com, 1 (call for heat), and 2 (satisfied). Given that the new thermostat doesn't have an earth terminal, can I use the three wires from the old Satchwell? If so, how would they be connected?
Back to top
 Alert Moderators

If you do not want to see this advert, click here to login or if you are new click here to join free.
gaswizzard

from United Kingdom

Joined: 08 Oct 2011
Posts: 6277
Location: Hertfordshire,
United Kingdom
Thanked: 987 times

PostPosted: Sun Nov 20, 2011 1:02 am Reply with quote

You only need com & 1 , i take it you have an S plan?
Back to top
The following user says thank you to gaswizzard for this useful post:
StrikeThree (20 Nov 2011)
 Alert Moderators
StrikeThree

from United Kingdom

Joined: 20 Nov 2011
Posts: 4
Location: Middlesex,
United Kingdom

PostPosted: Sun Nov 20, 2011 11:08 am Reply with quote

Thanks for the reply.
I'm not really sure, but I think it's an S plan. There's a motorised valve with water in and water out near the cylinder, and another of the same type near the boiler.
So I should forget about the present earth wire and just use the red and blue to connect to com and 1 on the new thermostat. It doesn't matter whether red goes to com or 1. Is that correct?
Back to top
 Alert Moderators
D_Hailsham

from United Kingdom

Joined: 18 Oct 2007
Posts: 8837
Location: Sussex,
United Kingdom
Thanked: 1029 times

PostPosted: Sun Nov 20, 2011 11:23 am Reply with quote

You don't need an earth wire, so make it safe at both ends

Although it doesn't matter in practice which way round the wires are, it's better to have them the correct way round as it makes life easier if you have to fault-find.

One wire will have 240V on it when you turn HW on at the timer; this should go to the Common terminal. The other wire connects to 1.
Back to top
The following user says thank you to D_Hailsham for this useful post:
StrikeThree (20 Nov 2011)
 Alert Moderators
StrikeThree

from United Kingdom

Joined: 20 Nov 2011
Posts: 4
Location: Middlesex,
United Kingdom

PostPosted: Sun Nov 20, 2011 11:06 pm Reply with quote

Thanks for the help.
Is it likely that the CH system, or part of it, is getting its earth from the hot water cylinder via the wire to the chassis of the cylinder thermostat that I am about to replace?
Back to top
 Alert Moderators
D_Hailsham

from United Kingdom

Joined: 18 Oct 2007
Posts: 8837
Location: Sussex,
United Kingdom
Thanked: 1029 times

PostPosted: Mon Nov 21, 2011 11:28 am Reply with quote

StrikeThree wrote:
Thanks for the help.
Is it likely that the CH system, or part of it, is getting its earth from the hot water cylinder via the wire to the chassis of the cylinder thermostat that I am about to replace?

Very unlikely. The earth wire is only there for the thermostat and the new stat does not need an earth. In any case the cylinder will be earthed via the copper pipes back to the boiler and any other component which has an earth wire, e.g the pump.
Back to top
 Alert Moderators
StrikeThree

from United Kingdom

Joined: 20 Nov 2011
Posts: 4
Location: Middlesex,
United Kingdom

PostPosted: Mon Nov 21, 2011 11:43 am Reply with quote

Many thanks.
I've got the information I need now to make the replacement.
Back to top
 Alert Moderators
Search this topic :: View previous topic :: View next topic  
Post new topic   Reply to topic    DIYnot.com Forum Index > Plumbing and Central Heating All times are GMT
Page 1 of 1

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
Similar Topics   Replies   Views   Posted 
Cylinder thermostat wiring advice 8 160 Thu Mar 31, 2011 11:22 pm
Honeywell T70 Hot Water Cylinder Thermostat wiring question 2 1020 Wed Jun 30, 2010 11:14 pm
New hot water cylinder thermostat - Wiring help 12 21860 Tue Feb 24, 2004 2:41 pm
Cylinder thermostat wiring 8 11220 Mon Nov 13, 2006 2:52 pm
Installing and Wiring a Potterton PTT2 Cylinder Thermostat 3 1400 Mon Feb 18, 2013 7:41 pm


 
DIYnot
Find an Expert | Find a Supplier | Search DIYnot.com
Network | Advertising | Newsletter
DIY | DIY How To | @home | DIY Wiki | DIY Forum
By using this site you agree to our Terms of Service / Disclaimer.
Please read our Privacy Policy. Copyright © 2000-2014 DIYnot Limited.