boiler timer or thermostat help please

[so1o]

Hello people

I need some advise and hope someone can point me in the right direction.

I just moved into a new house and the boiler fitted is a Potterton Suprima 70 (condensing boiler) as far as i know.

Next to the boiler is a Honeywell timer model ST6300A

Downstairs in the hallway is a manual thermostat model T6360B /(T40)

The Honeywell timer will only let me set the water or heating to come on together for the same amount of time. It wont let me for example set the water to come on for 1 hour and the heating to come on for 2 hours. The will both come on for the same amount of time in the am and pm time.

idea 1. I want to be able to set the water seperately and the heating seperateley.My first thoight was replace the boiler timer with a Honeywell ST9400C which would let me control the on and of time of the water and heating individually.

idea 2. After some reading on various forums including this one, a new idea was thrown in the mix. Leave the boiler timer as is and replace the thermostat in the hallway for a newer progrsmmable one. I can then use the boiler timer to control the water time and leave the heating on constantly which will be controlled by the new programmable thermostat.

What i want to know is there any benefit in idea 2 over idea 1? As far as i could work out the advantage would be i will have a newer thermostat that will be digital, programmable and more accurate? Am i right in assuming this or should i leave the thermostat as is and replace the boiler timer? If i should replace the thermostat what do you recommend? As long as its programmable and digital i will be happy.

Both the boiler timer and thermostat work properly, i dont know how accurate the thermostat is but it does work.

Please help and thanks in advance

For reference this is how my thermostat is wired up.

brown wire to terminal 1
green/yellow wire to terminal 3
blue wire to terminal 2

 

[D_Hailsham]

Option 1 will overcome the HW and CH timing problems, but you would still be left with a mechanical thermostat which relies on outdated technology.

Option 2 is probably the better bet as it will solve the timing problem and provide you with a more accurate thermostat. A programmable thermostat also incorporates features which are not available when programmer and thermostat are separate items. The most important of these is 'optimization', which automatically adjusts the boiler on time according to how warm/cold it is.

As for makes and models, the Honeywell CM901(24 hr) or CM907 (7 day) are normally considered the best.

However it's not just a case of replacing the existing thermostat with a programmable one. You need to modify the wiring of the existing timer so it no longer controls the CH. It's a simple job : you just disconnect the wire from terminal 4 (CH ON) and connect it to terminal L. This is the same wire as the brown connected to terminal 1 of the existing thermostat.

Assuming a Honeywell, the wiring would be as follows:

Old - New
1 - A
2- not used: make safe,e.g in a terminal block behind the wall.
3 - B

The green/yellow wire in 3 is being used as the switched live to the boiler. This does not comply with wiring regulations as a green/yellow wire is reserved for 'earth' wires. Unfortunately this was frequently done as it was more convenient. It would be a good idea to put some red sleeving or insulating tape round this wire to show that it is a 'live' wire.

 

[so1o]

Hi,

Thanks a lot for the advice. Option 2 is what i had in mind. However i wanted to use the CM927 model which is the same as you mention but wireless. Correct?

Anyone else got an opinion?

Thanks

 

[D_Hailsham]

However i wanted to use the CM927 model which is the same as you mention but wireless. Correct?

Yes, the CM927 is the wireless version of the CM907.

I've had a CM927 for over five years and never had any problems.

The receiver part of the CM927 could be mounted in place of the existing thermostat, using the existing wiring, or near the wiring centre with a new cable from the receiver to wiring centre.

Come back if you need help with the wiring (When you have made up your mind ).

 

[so1o]

Thanks man willdo i got other issues to sort out lol.

£200 gas bill in one month...

 

[so1o]

Hi People

Sorry to revive an old thread but it still applies.

Finally got my act together and have got myself a sundial rf pack 2.

ST9420C and DT92E.

Now i managed to replace my ST6300A with the ST9420C as it was a direct replacement, it fitted perfectly over the previous base plate.

Now the hot water worked when i switched it on but the heating would not work. The red light on the ST9420C would come on indicating that its working etc but the heating would not fire up. The old thermostat was left in situ so i disconnected the wiring for this but still had the same fault. What wiring needs to be changed so i can make use of the wireless thermostat and get rid of the old thermostat.

If you need more information please let me know.

 

[gaspro1981]

Have u got a gravity hw pumped central htg set up ??

 

[so1o]

Let me describe it as i have no idea.

Potterton suprima 70
Hot water tank
pump

Pretty sure its a gravity pumped system.

I have a pump on my shower to make it work properly. Not an electric shower.

 

[Boilerman2]

The Suprima is a fully pumped boiler it cannot do Gravity - so yours is without the shadow of doubt fully pumped

 

[so1o]

Goes to show what I know lol.

Sorry for wrong info.

 

[amypie]

Hi I want to do similar thing for different reason...
I have Worcester Bosch Combi boiler, with built in mechanical timer - the timer does not work.
I have a mechanical room thermostat (Honeywell T6360B) so I want to replace it with a new programmable one (probably a Honeywell CM907/707). I checked existing wiring, it's the same as so1o's photo at the thermostat, except I have grey wire to both 2 and 3.

What threw me is behind a blank plate next to boiler labelled "thermostat". There's a terminal block with Blue, G/Y, Brown from one direction, and Grey, Black, Brown (and an earth that is snipped, not terminated) from another.

Does anyone know what this and what affect it could have on wiring the thermostat? I was all set to use existing wires (1) and (3) but now I feel unsure where each wire is routing to/from. Any advice??

Thanks!

 

[Ackoman]

However it's not just a case of replacing the existing thermostat with a programmable one. You need to modify the wiring of the existing timer so it no longer controls the CH. It's a simple job : you just disconnect the wire from terminal 4 (CH ON) and connect it to terminal L. This is the same wire as the brown connected to terminal 1 of the existing thermostat.

Sorry to revive old thread - regarding the above, can't the existing timer just be set to continuous?

 

[JohnD]

Yes.

 

[D_Hailsham]

Sorry to revive old thread - regarding the above, can't the existing timer just be set to continuous?

Moving the wire from 4 to L eliminates the possibility of the heating being turned off by some well-meaning person fiddling with the old programmer.