Seperate Hot Water to Heating control

[goble]

Our old Landis & Gyr RWB2 programmer would not let us have the heating on without the hot water being on.
I thought this was because of the programmer itself so I bought a digital Seimens RWB29 that goes on the same backplate to replace it in the hope it would give me seperate control of both CH & HW.
I have put the programmer on Mode 16 which I think should allow seperate control, the heating does not work on its own, but the hot water does.

Can anyone tell me if this is because it needs to be wired differently or could it possibly be a problem with the system itself, such as the pump/valve?

 

[TicklyT]

Is your system fully pumped, or gravity hot water?

Older systems were set up without motorised valves, relying on gravity circulation to heat the hot water. The clock switched the boiler for hot water, and the pump for heating.
As it's pointless running the heating pump with the boiler turned off, there was an interlock on the clock to stop you selecting heating on, hot water off.

Fully pumped systems have two 2-port valves or a 3-port valve, a room stat and a cylinder stat, all wired to allow individual selection and control of heating and hot water.

Wiring faults, valve or thermostat failures could all result in the symptoms you describe.

 

[goble]

I believe the system is fully pumped.

When we had an engineer in to service the boiler he had a qucik look and said we should only need to change the programmer. He mentioned that he thought he could hear a valve trying to open for the central heating when he tried something (not sure what), therefore not sure whether it is the valve or not.

Would there be a different wiring to have it setup between having seperate CH and HW or where you have to have the HW on with the CH?

 

[D_Hailsham]

Do you have ONE valve as in LEFT Pic, or TWO valves as in RIGHT Pic? The valves are normally near the hot water cylinder.

View media item 5946 View media item 11762

 

[goble]

Below is a picture of the valve.

Untitled

• goble
• 17 May 2010
• 1

 

[D_Hailsham]

Thanks for the pic of the valve. It's a 3-port valve, which means you have a Y-plan system.

Turn the power to the system off completely (setting the timers to off is not enough). This resets the valve to default position. The lever on the right should be at the Auto end of the slot.

Move the lever to the Man end of the slot. You should feel some resistance as you are pushing against a spring. When you get to the Man end, let go of the lever and it should move back to the Auto end.

If the lever gives no resistance or does not move back when released, the valve is sticking. You may be able to correct this by removing the actuator (metal box) and lubricating the valve spindle with a small amount of WD40 or similar. The spindle will not make a complete rotation, just turn about 20 degrees.

If the lever moves across with resistance and returns ok, the problem will be electrical.

You can find full info on testing the valve, timer and thermostats Here.

 

[goble]

Many thanks for your reply D_Hailsham. I have moved the lever to the manual end and I felt the resistance from the spring ,when released it moved back smoothly.

If it is an elecetrical problem do you have an idea what it might be?

 

[Tibbot]

Many thanks for your reply D_Hailsham. I have moved the lever to the manual end and I felt the resistance from the spring ,when released it moved back smoothly.

If it is an elecetrical problem do you have an idea what it might be?

It seems set up for no CH only. Seen it on fully pumped systems but never wired one up in this way. Your best bet is to buy a decent junction box like the Drayton LWC, download y-plan diagrams and re-wire to suit.

 

[D_Hailsham]

It seems set up for no CH only. Seen it on fully pumped systems but never wired one up in this way. Your best bet is to buy a decent junction box like the Drayton LWC, download y-plan diagrams and re-wire to suit.

That's a distinct possibility.

The Honeywell or similar 10 terminal wiring centre is just as good. Here is the wiring diagram

View media item 70

 

[goble]

Looking at the wiring diagram I think my system does need to be rewired, as on the baseplate it currently has connections to only HW ON and CH ON and nothing to HW OFF.

Me and electrics don't really mix so I may need to get someone in to get it done.
Does anyone have any idea how much it may cost to have the wiring changed?

 

[D_Hailsham]

Looking at the wiring diagram I think my system does need to be rewired, as on the baseplate it currently has connections to only HW ON and CH ON and nothing to HW OFF.

That is probably the cause of the problem but, to be certain, can you post the part number of the motorized valve?

Me and electrics don't really mix so I may need to get someone in to get it done.
Does anyone have any idea how much it may cost to have the wiring changed?

It should not take a competent person more than a couple of hours so £50-60. Make sure the person is fully conversant with wiring central heating systems; many electricians don't have a clue.

 

[goble]

I'll have look when I get home and let you know the part no. cheers

 

[goble]

Why do they always have to put the information you need in the most inacessable places, like an inch from the cylinder at the back of the cupboard.

Anyway, the valve is a Honeywell V4073A 1039

 

[D_Hailsham]

the valve is a Honeywell V4073A 1039

In that case, your problem is caused by the missing wire(s).

If you look at the diagram carefully you will see that there are three wires connected to terminal: grey from valve; timer HW OFF; cylinder thermostat sat terminal. So the cylinder stat has three wires connected. You say that the wire to the timer HW OFF is missing. What about the cylinder stat, are there three wires connected or just two? If only two, you need to add the third wire as well.

 

[goble]

I checked the wiring to the diagram and the wire for timer HW OFF is not anywhere to be seen.

I think there is 3 wires from the cylinder, the wires from the cylinder are connected as follows

Yellow - Cylinder
Grey - Valve
(No timer wire connected with these)

Red - Cylinder
Black - Timer Controller

Blue - Cylinder
Orange - Valve
Black - Boiler

The wiring diagram shows there should be a live from the Pump connected to the blue,orange,black above but there isn't. The blue live from the pump is connected seperately with the blue live's from the boiler and time controller.

Not sure this makes sense but it's the best I could do.