Programmer replacement confusion

[Gorbash12346]

I am having some issues swapping from an old 24 hour mechanical programmer to a new 7 day programmer.

The old programmer is a siemens RWB2E

and the new programmer is a Drayton LP722

The issue I have is with the wiring. (we have just had a full re-wire done and apparently none of the central heating system was included in this. Normal practice?)

currently the pins on the back plate that are in use are N,L, 3 and 4. and the controller has this diagram on the back

The new programmer has this on the back

my understanding was that i needed to use pin 2 and pin 4 to allow me to switch on and off however with pin 4 where it is and the previous pin 3 moved to two all i get is the central heating pump turning on and the boiler won't ignite. reversing them ignites the boiler but leaves the pump off.

would this suggest that both need to be on pin 4?, in which case how would the off signal work? Unfortunately I don't know what the layout is but I have an old Honeywell room thermostat as well.

The boiler I have is very old ideal mexico system boiler which I am being told I cannot heat DHW separate from CH. This is fine if a little annoying as I am saving for a new boiler but is this correct?

Apologies home electrics and central heating systems are completely new to me, (first house) so any and all help would be very much appreciated!

Thanks!

 

[stem]

my understanding was that i needed to use pin 2 and pin 4 to allow me to switch on and off

No, that's not right, you will not need terminal 2 at all, and you will only need terminal 1 if you have a 'Y Plan' system with a three port motorised valve. And as there was not a connection to 1 originally, this would not be the case.

If you look at the diagrams you can see that the two programmers have identical connections, they are a straight swap.

N=N
L=L
1 not used
2 not used
3=3
4=4

 

[Gorbash12346]

Ok I had tried that but found I could only get the boiler to turn on when I switched on the DHW side. I'll give it another try and see if I've missed something.

Thanks!

 

[stem]

Maybe you have a gravity hot water system with only the central heating pumped. Is this the case?

If so:

For hot water you switch on the hot water and only the boiler works, and the water circulates naturally around the hot water cylinder.

For central heating, the programmer is wired to the pump to circulate the water around the radiators, but you will also need the hot water to be 'on' to make the boiler operate as well.

There is a link on the back of the programmer to set it to 'Fully pumped' or 'Gravity' according to the system you have.

If you have something else such as a system with motorised valves post back what you have.

 

[Nozzle]

Plus the boiler switching and pump running (on my S-plan any way) is controlled via the microswitch in the valve head.

Timer opens valve if thermostat is not satisfied

Open valve makes limit switch

Limit switch fires pump and boiler

Thermostat eventually is satisfied

Valve closes, limit switch is not made, boiler shuts off

Pump shuts off once boiler thermostat is clear

Nozzle

 

[Gorbash12346]

Apologies yes that is the case (hot water pressure at the taps is abysmal)

The drayton programmer has a jumper on the back for pumped and gravity now that I'm looking at it. Is it simply a case of moving that over to gravity but keeping the wiring the same?

Thanks!

 

[stem]

Apologies yes that is the case (hot water pressure at the taps is abysmal)

That is irrelevant, the pressure at the taps depends upon the height of the feed tank supplying the hot water cylinder and is nothing to do with how the boiler heats it up. So are you sure you have a gravity (ie naturally circulating and not pumped) hot water system?

Is it simply a case of moving that over to gravity but keeping the wiring the same?

Yes, all that it changes is when you select central heating, it will also switch on the hot water which has also to be on to operate the boiler.

 

[stem]

Plus the boiler switching and pump running (on my S-plan any way) is controlled via the microswitch in the valve head.

The OP has stated that the boiler is operating, so if he has a motorised valve (and that's in question) the limit switch is working.

 

[D_Hailsham]

The boiler I have is very old ideal mexico system boiler which I am being told I cannot heat DHW separate from CH. This is fine if a little annoying as I am saving for a new boiler but is this correct?

Yes, it's correct; you have a semi-gravity system. The Drayton programmer should be set to G.

Wiring is exactly the same as the Siemens: L=L, N=N, 3=3, 4=4.

If the backplates are identical, you just have to unclip the Siemens and replace it with the Drayton.

Correction: In the winter you can't have CH without HW; but, in the summer, you can have HW without CH.

 

[Gorbash12346]

That helps a lot thankyou all very much! I'll give it another try with the jumper in the gravity position and hopefully that's all that's needed for now.

 

[Gorbash12346]

I've just tried it with the wiring in the original positions and the jumper moved over to gravity fed. All seems to be working as it should. Thanks!