Re: Boiler Timer and Room Thermostat work independently

[rojroj]

Hi there,

When my Boiler Timer is ON, then the Boiler runs irrespective of what the Thermostat setting is (even if the setting is lower than the room temp).
However, when it is OFF, the Thermostat takes over and works (turns Boiler ON only if the setting is higher than the room temp).
Shouldn't they work in conjunction rather than either this or that (like for the Boiler to be ON, both the Timer needs to be ON and the room temp needs to be lower than the Thermstat setting) ?
This is a new house we have moved in, so can't tell if it ever worked or stopped working recently.

I suspect it is wired wrongly (they are in parallel ?) as each seems to work independently.

Any help / advice highly solicited.

 

[Puddle]

First thing to check is that the room thermostate you are talking about,is not a frost thermostat,designed to bring boiler on ,when heating off, when it gets could,if that is not the case maybe it was or has been changed,for a normal thermostat

However the following may correct siduation to allow thermostat to be used when heating on

You do not say what programmer it is but will have a ‘heating off’/’heating on’ terminal on back plate, pursume on’ heating on’ connection, switch live to boiler or motorised valve, on 'heating off’ position, switch live going through room thermostat to boiler /motorised valve.
Try removing wire from 'heating on’ terminal and make safe by fitting in a strip conector, then removing wire from 'heating off ‘and placing in 'heating on ‘terminal.

This should allow switch live from programmer to run through room thermostat when programmer turned to ‘heating on’ and then to boiler thus controlling heating by programmer and thermostat

But then again....

 

[rojroj]

Thanks Pudle for the advice.
The Timer is a Honeywell 6400C with 3 On/Off and 7 day setting.
I have tried to reset and change the settings - no luck.
The Thermostat is a room thermostat (Honeywell - Electronic) which shows the room temp and has two press buttons to set the temp (one for raising, one for lowering). It works fine when the Timer is Off, ie turns the Boiler On only when the room temp falls below the setting.

I opened the Timer and checked the connections.
Apart from the Ground, it has 5 wires connected :

Live, Neutral, HW ON, HW OFF, CH ON

Note that the CH OFF is not connected (and the manual says that is a valid connection for Y Plan). Now I don't understand what a Y Plan is, so not sure here. My local CH Engineer said that the CH OFF is never connected.

Would you still suggest that I disconnect the wire from CH ON and connect it to CH OFF ?

 

[Puddle]

Would you still suggest that I disconnect the wire from CH ON and connect it to CH OFF ?

I did not suggest above,I suggested the other way round,however you say you do not have anything connected to 'heating off' at present are you getting mixed up with hot water off,hot water off provides power for 'y'plan,heating only mode

imho

 

[rojroj]

Sorry for the confusion, let me clarify.

The connections are as below :

'GND' 'Neutral' 'Live' 'HW Off' 'CH Off' 'HW On' 'CH On'

The only terminal not connected is 'CH Off'.

The Thermostat is actually a Drayton Digistat 1 and the Boiler is a Potterton Suprima. There is a Hot Water Storage Tank with a Diverter Valve (is that what a Y Plan means) ?

After lot of tweaking around, it seems to have changed its behaviour a bit.
Now, it doesn't turn on when the Timer is OFF (even if the Thermostat asks it to) - so that is good.

However, the other problem is still there - it turns ON when the Timer is ON even if the Thermostat doesn't ask for it (ie even if the temp is high enough).

 

[rojroj]

I suspect the Thermostat is wired incorrectly (so it might have replaced a frost Thermostat or another room thermostat).
I have replaced the Batteries.
I checked the suggested Elecrical Connections for a Drayton Digistat 1 and it says :
1 - Common, 2 - Satisfied and 3 - Demand.
However, on mine, 2 is not connected.
Only 1 (red) and 3 (yellow) are connected.
On the wall, there is a note saying :
1 - red, 2 - blue, 3 - yellow, etc

Do I need to connect the Blue wire to Terminal 2 (Satisfied) ?

Please suggest if there is any risk in trying this.

Also, I probably posted this in the wrong Forum - can this be moved to the main Central Heating Forum pls from the Plumbing Tools Forum ?

Thanks

 

[Puddle]

often when wiring is mixed up it is easier to disconnect every thing and rewire from scratch,following wiring diagram of what ever diverter valve you have in the system

 

[doitmyself]

The connections are as below :

'GND' 'Neutral' 'Live' 'HW Off' 'CH Off' 'HW On' 'CH On' The only terminal not connected is 'CH Off'.

There is a Hot Water Storage Tank with a Diverter Valve (is that what a Y Plan means) ?

The first thing is to identify what type of valve you have.

There are two types of 3-port valves: the diverter and the mid-position. However many people refer to both as diverter valves. A Y-plan uses a mid position. What is the valve make and model number?

You can sometimes tell which valve you have by the wires. The diverter's are brown, blue, grey and orange (plus earth) and a mid-position's are white, blue, grey and orange (plus earth).

I checked the suggested Elecrical Connections for a Drayton Digistat 1 and it says :
1 - Common, 2 - Satisfied and 3 - Demand.
However, on mine, 2 is not connected.
Only 1 (red) and 3 (yellow) are connected.
On the wall, there is a note saying :
1 - red, 2 - blue, 3 - yellow, etc

Do I need to connect the Blue wire to Terminal 2 (Satisfied) ?

If you have a mid-position valve there should be a connection to the Sat terminal.

But you must find out where the other end of the blue wire connects first. It could be a left over neutral from the previous thermostat. If you just connect this to the Digistat you will, at a minimum, blow a fuse and could blow the programmer and digistat.

 

[rojroj]

Thanks 'doitmyself' for the reply.

I think it is a mid position one as there is a dial (which can be turned) and 'mid position' is written underneath it.
Can I turn the dial to check ?

I suspect the Blue wire to be Neutral - as the old connections had a Red (Live), a Yellow/Green (Ground), a Yellow (Switched Live ?) and a Blue (Neutral ?).

But how can I be certain ?

If the 2nd (Sat) should have a wire, as suggested by Drayton, where would it come from ?

Also, should both the Red and Yellow be Live when the CH is ON (I have checked it with a tester with the stat removed from the wall mounted back plate). I thought the stat would switch the connections to either 2 or 3 depending on whether the room temp is satisfied or not

Regards

By the way, I can hear the stat click when I set the temp above or below the room temp - which suggests that the relay is working.
I replaced the batteries.
Before I replaced them, it had another problem (in addition to the existing one) : when the CH was OFF, the Boiler could be turned OFF or ON by changing the stat setting !

 

[doitmyself]

I think it is a mid position one as there is a dial (which can be turned) and 'mid position' is written underneath it.
Can I turn the dial to check ?

If it says 'mid position' I think we can accept that it is. However I have never heard of a valve with a dial. What is the valve make and model? Can you post a pic of the valve?

I suspect the Blue wire to be Neutral - as the old connections had a Red (Live), a Yellow/Green (Ground), a Yellow (Switched Live ?) and a Blue (Neutral ?). But how can I be certain ?

If, by 'old connections', you mean the previous thermostat, then the blue wire is very probably the neutral. Mechanical thermostats needed a neutral connection to improve their accuracy; but modern battery operated digital thermostats do not need a neutral.

If the 2nd (Sat) should have a wire, as suggested by Drayton, where would it come from?

Are you talking about the digistat? If , so the SAT terminal should not have anything connected to it. (I made a mistake in my last post - I was thinking of the cylinder stat when I wrote: "If you have a mid-position valve there should be a connection to the Sat terminal.")

Also, should both the Red and Yellow be Live when the CH is ON (I have checked it with a tester with the stat removed from the wall mounted back plate). I thought the stat would switch the connections to either 2 or 3 depending on whether the room temp is satisfied or not

That does not sound right. The stat should connect 1 to 3 or 1 to 2. If the stat is removed there should be 240v on 1 when CH is ON at the programmer. Terminals 2 and 3 should have 0v.

Before I replaced them, it had another problem (in addition to the existing one) : when the CH was OFF, the Boiler could be turned OFF or ON by changing the stat setting !

[/quote]
You need to check where the other end of the wire to Digistat terminal 1 connects. It should be to Programmer terminal 4 (CH ON).

Remove the programmer from the wall and see if the problem remains or goes away.