Ask The Trades - Grant Combi 90 Mk 2 : wireless thermostat problems

Welcome, Guest. Please Login or Register

	Jun 15^th, 2026, 11:24am
View recently thanked users View top thanked users

Quote: A rock --> me <-- A hard place

Ask The Trades › DIY Forum › Electrical Questions › Grant Combi 90 Mk 2 : wireless thermostat problems

(Moderator: Lectrician) - (Moderator Group: Board Moderator)

< Previous Topic | Next Topic >

Pages: 1

Grant Combi 90 Mk 2 : wireless thermostat problems (Read 8844 times)

apsimpson

GDPR opt-out

Grant Combi 90 Mk 2 : wireless thermostat problems
Sep 6^th, 2010, 7:24pm

I have a Grant Combi 90 Mk 2 oil boiler which has a mechanical timer that does provide enough heat when needed. But need to add thermostate control. So I thought a wireless programmable thermostst would be easily enough sorted. First I bought a sunvic TLX RFP afer peaking to Sunvic. As the TLX RFP only has one control wire, this failed. Grants couldnt offer any help. Does anyone know of a wireless programmable thermostat that does not cost the earth?

IP Logged

Lectrician Administrator Trade Member Author Offline Ask The Trades Posts: 8815 Total Thanks: 109 For This Post: 0 Braunton, North Devon United Kingdom Gender: Trade: Electrician	Re: Grant Combi 90 Mk 2 : wireless thermostat problems Reply #1 - Sep 6^th, 2010, 8:07pm I am not really sure I understand what you mean. What do you mean by "one control wire"? Are you trying to ditch the old time clock in prefference to a stat? Does the current clock do more than heating (water?). Do you currently have a room stat and cabling? Photos may help.
Back to top	Need to post a picture? Click HERE for info! IP Logged

CWatters

Super Member

Offline

"Daddy fick it" says James

Posts: 5150

Total Thanks: 58
For This Post: 0

Gender: male

Re: Grant Combi 90 Mk 2 : wireless thermostat problems
Reply #2 - Sep 7^th, 2010, 6:40pm

I think I understand the problem...

The wiring diagram for the Grant assumes that the stat is a "volt free type" - See pins 4 and 5 on the terminal block page 50.

http://www.grantuk.com/userfiles/download_81.pdf

Some stats have "volt free outputs" eg two output signals that are either connected together by a relay in the stat or open circuit depending on the room temperature.

The Sunvic only provides a single "Call for heat" signal that is either 0V or 230V depending on the room temperature.

Solutions:

There is probably a way to connect the Sunvic directly to the Grant but I'd need more time to think about it.

It could be done using a relay to convert the single "call for heat" signal to "volt free".

or you could find another wireless stat that provides "volt free outputs".

IP Logged

CWatters

Super Member

Offline

"Daddy fick it" says James

Posts: 5150

Total Thanks: 58
For This Post: 0

Gender: male

Re: Grant Combi 90 Mk 2 : wireless thermostat problems
Reply #3 - Sep 7^th, 2010, 7:30pm

Ok I can't see how to connect the sunvic directly to the Grant without using a relay. Perhaps best look for a wireless stat with volt free outputs.

Caution: If you just connected the Sunvic "call for heat" signal into terminals 5 it might appear to work BUT I think that would be dangerous. It appears that doing this would bypass the internal overheat/limit thermostat and the pressure switch!

It appears the route "live" takes around the control system is...

Incoming Live Pin 3
Boiler on/off switch
Pin 12
Pressure Switch
Pin 13
Limit Thermostat
Pin 10
Relay 1
Pin 4 (Comment: live only reaches this point if boiler is safe to fire up)
Link (or via the room stat to)
Pin 5
Heating Switch
Pin 7 (or Pin 7 via built in timer depending on heating switch position)
Relay 2 and onwards to the inner workings of the boiler.

« Last Edit: Sep 7^th, 2010, 8:11pm by CWatters »

IP Logged

CWatters

Super Member

Offline

"Daddy fick it" says James

Posts: 5150

Total Thanks: 58
For This Post: 0

Gender: male

Re: Grant Combi 90 Mk 2 : wireless thermostat problems
Reply #4 - Sep 7^th, 2010, 8:26pm

Cheapest wireless programable stat I can quickly google up is the Siemens RDJ10-RF for £55 inc vat from several places including..

http://www.heatingcontrolsonline.co.uk/siemens-rdj10rf-wireless-programmable-roo...

Screwfix also have it at £66.69. Personally I think it looks a bit ugly. Screwfix also appear to have an older version(?) of the same stat at £51 but not all the reviews are good. Some say battery life is poor.

I don't think the £60 Horstman HRFS1 is volt free.

I'd save up and get a Honeywell or Heatmiser but they are £90-£120.

« Last Edit: Sep 7^th, 2010, 8:27pm by CWatters »

IP Logged

Pages: 1

(Moderator: Lectrician) - (Moderator Group: Board Moderator)

< Previous Topic | Next Topic >

Ask The Trades › DIY Forum › Electrical Questions › Grant Combi 90 Mk 2 : wireless thermostat problems