Drayton LP722 Thermostat Wiring Diagram
Drayton LP722 programmer wiring
Wall plate with the 230 V mains and the hot water (HW) and central heating (CH) outputs.
Terminals and components · 7
- Live
- Neutral
- HW OFF
- CH OFF
- HW ON
- CH ON
- P/G link
Connection
Run the neutral from the same 230 V AC, 50 Hz circuit that feeds terminal L. The equipment the programmer controls takes its neutral from the junction box, not from this terminal.
Function
Inside the programmer, L feeds the clock and the commons of both changeover switches. That's why terminals 1 to 4 deliver 230 V when their switch is closed; no link is needed.
Caution
- Installation must only be carried out by a qualified electrician or heating engineer.
- Switch off the mains before starting and before removing the unit; never fit it to a live wall plate.
- The mains input must have a 3 A fuse.
- Fixed wiring only, in line with current wiring regulations.
Earth
The unit is double insulated and needs no earth; the wall plate has an earth loop terminal to keep the cable's earth continuous.
Connection
Use it only if the system needs a signal while hot water is off, for example the "hot water off" input of a three-port mid-position valve. Otherwise leave it free.
Caution
- The output delivers the 230 V live from L: don't use it to switch low-voltage circuits.
- Rating of each switch: 2(1) A at 230 V AC.
Connection
Usually left free. Use it only if some equipment must be powered while heating is off.
Caution
- The output delivers the 230 V live from L: don't use it to switch low-voltage circuits.
- Rating of each switch: 2(1) A at 230 V AC.
Connection
Run this terminal to the system junction box, towards the cylinder thermostat and hot water valve, which in turn call the boiler and pump.
Tip
Consult the boiler handbook for pump overrun wiring details.
Caution
- The output delivers the 230 V live from L: don't use it to switch low-voltage circuits.
- Rating of each switch: 2(1) A at 230 V AC.
Connection
Run this terminal to the system junction box, towards the room thermostat and heating valve, which in turn call the boiler and pump.
Tip
Consult the boiler handbook for pump overrun wiring details.
Caution
- The output delivers the 230 V live from L: don't use it to switch low-voltage circuits.
- Rating of each switch: 2(1) A at 230 V AC.
Settings
Setting System Operation P Fully pumped and controlled Heating and hot water are set separately. G Gravity-fed hot water Heating can't run without hot water; hot water can run alone. Tip
The LP722 allows a different program for each day of the week, with independent heating and hot water timing in the P setting.
Check
Set the link to the system type before fitting the programmer to the wall plate.
About This Diagram
This diagram is redrawn from pages 2–3 of the Drayton LP722 Thermostat Installation Instructions, and we offer it completely free and in English. We have also categorized it in the Thermostats (HVAC & Water Heating) section on Diagramverse, and it has been rated by 1 user with an average rating of 5.0. If you have any specific questions about the Drayton LP722 Thermostat Wiring Diagram, we suggest checking the Frequently Asked Questions (FAQs) section.
Printable Drayton LP722 Wiring Diagrams
Wiring Instructions
Before you start
The Drayton LP722 is a mains-powered, dual-channel programmer. It runs on 230 V AC and switches 230 V to your hot water (HW) and central heating (CH) circuits. Installation should be done by a qualified electrician or heating engineer. Your local wiring regulations apply, and in the UK that means BS7671. The unit is designed for fixed wiring only, so never feed it from a plug and flex.
- Supply: 230 V AC, 50 Hz, from a fused spur or mains isolator with a 3 A fuse. Do not use a higher fuse rating.
- Tools: an insulated terminal screwdriver, a voltage tester or a multimeter rated for mains voltage, wire strippers, a drill and wall plugs, or M3.5 x 14 bolts for a conduit box.
- Cable: the sources do not give a conductor size. As general good practice, use fixed-wiring cable suitable for a 3 A fused circuit and the terminal size on the wall-plate. If you are not sure, follow your local regulations.
- Mounting: leave 70mm clear to the right of the wall-plate and 25mm above it, plus room underneath to reach the securing screws. Mount the plate with the terminals at the top, either directly on a flat wall (No. 6 x 1" screws) or on a flush single conduit box type UA1 (BS4662). Do not use a surface mounting box. A good position is about 1.4m above the floor, away from condensation and extreme temperatures.
- Isolation: switch off and lock off the mains isolator, then prove the wall-plate terminals are dead with your tester. Never fit the programmer onto a live wall-plate.
Which wiring applies to you: the diagram shows the programmer's own terminals. How the outputs continue through the junction box depends on your system: a mid-position valve system, a two-valve spring-return system, or gravity hot water with pumped heating. Find out which one you have before you start. You will also need the boiler handbook if the boiler has pump overrun.
Step-by-step wiring
- Switch off the mains and prove it is dead. If you are replacing an old programmer, loosen its securing screws and unplug it from the wall-plate.
- If you are reusing an existing wall-plate, check the old model against Drayton's terminal comparison chart. Many industry-standard plates already use the N, L, 1, 2, 3, 4 layout and need no rewiring. Others need their wires moved, and any old links between terminals must be removed.
- For a new wall-plate, fix it level with the terminals at the top. For surface wiring, snap out the cable entry strip on the bottom edge.
- Connect the incoming mains neutral to N and the fused live to L. Terminal L powers the clock and the common of both the HW and CH switches. No separate link is needed.
- Connect 3 (HW ON) to the hot water call. Depending on your system, that is the cylinder thermostat or the hot water side of the junction box.
- Connect 4 (CH ON) to the heating call. Depending on your system, that is the room thermostat or the heating side of the junction box.
- Connect 1 (HW OFF) and 2 (CH OFF) only if your system diagram uses them. Some mid-position valve layouts need a 230 V signal when hot water is off. Fully pumped two-valve systems often leave these terminals unused.
- Terminate the earth conductors on the earth continuity (loop) terminal. The programmer is double-insulated and needs no earth itself, but earth continuity to the rest of the circuit must be kept.
- Set the P / G link on the back of the programmer. Use P for a fully pumped system where heating and hot water are controlled separately. Use G for gravity-fed hot water.
- Check every screw is tight and no bare copper shows. Then plug the programmer onto the wall-plate and tighten the securing screws.
Testing and start-up
Check that the fuse in the mains input is 3 A, then switch on. The display should light up. The clock comes set from the factory and adjusts itself for summer time. If the display stays blank, there is no supply at L and N.
Once the programmer is plugged in, you can't reach its terminals, so take your readings at the junction box or the thermostats:
- Use the HW SELECT button to choose ON. You should read about 230 V between the HW ON wire and neutral, and 0 V on HW OFF. Select OFF and the readings should swap.
- Repeat with the CH SELECT button for CH ON and CH OFF.
- With CH on and the room thermostat turned up, the valve should open and the boiler and pump should start. Do the same for hot water with the cylinder thermostat.
- Check that heating and hot water can each run on their own. On a P setting, heating alone should work. On a G setting, heating cannot run without hot water.
Last, set the timings and finish with the built-in TEST? routine. Return the switches to TIMED before you leave.
Safety notes
- Every output terminal carries 230 V when its channel is in that state. A terminal you are not using can still be live, so treat all six terminals as hazardous.
- Each switch is rated 2(1) A, which means 2 A resistive and 1 A inductive. Valve motors and pumps are inductive loads. Do not drive large loads directly from the programmer: run them through the junction box and the boiler's own controls as the system diagram shows.
- The heating system may have more than one supply, for example a boiler with pump overrun. Isolate every supply before you open the junction box.
- Always switch off the mains before you remove the programmer from its wall-plate.
Troubleshooting
| Symptom | Probable Cause | What to Check |
|---|---|---|
| The display is completely blank after I switch on | No 230 V at L and N: the 3 A fuse has blown, the isolator is off, a conductor is loose, or the unit is not fully seated on the wall-plate | Check the 3 A fuse and the isolator. With the power off, check the L and N screws. With the power on, measure about 230 V between L and N on the wall-plate before you refit the unit, then tighten the securing screws evenly. |
| The 3 A fuse blows when the system calls for heat or hot water | An output wire touches neutral or earth, or the connected load is more than the 2(1) A switch rating | Isolate the supply and check the wires on 1, 2, 3 and 4 for insulation resistance to N and E. Make sure the pump and boiler are fed through the junction box and the boiler's own controls, not directly from one programmer output. |
| Heating comes on when I select hot water, and hot water comes on when I select heating | The wires on terminals 3 HW ON and 4 CH ON are swapped | Select HW ON only and measure which junction box wire goes to 230 V. It should be the one to the cylinder thermostat or the HW valve. If not, swap the wires on 3 and 4. |
| I can't get heating without the hot water also coming on | The P / G link is set to G on a fully pumped system | Isolate the supply, remove the unit and move the link to P. Only gravity-fed hot water systems should be set to G. |
| The heating runs when the programmer shows it off, and stops when it shows on | The heating call wire is on terminal 2 CH OFF instead of 4 CH ON | With CH selected OFF, measure the room thermostat feed. It should be 0 V. If it reads 230 V, move the wire from 2 to 4. |
| Something runs constantly after I replaced an old programmer | An old wall-plate link is still in place, for example L to an output, or the old terminal layout was kept | Compare the old model with the terminal comparison chart. Remove any links the old unit needed and rewire to N, L, 1, 2, 3, 4 as shown. |
| The CH light is on but the boiler never fires | The heating call is lost after the programmer: the room thermostat is wired to SAT instead of CALL, or a junction box wire is loose | Measure 230 V at terminal 4 in the junction box, then at the room thermostat COM and CALL terminals with the thermostat turned up. Follow the circuit until the voltage disappears. |
| The hot water won't switch off on a mid-position valve system | Terminal 1 HW OFF is not connected where the system diagram needs it | With HW selected OFF, check for 230 V on terminal 1 and at the junction box terminal it should feed. Connect it as shown in the mid-position valve layout. |
| The boiler pump stops abruptly or the boiler overheat trips after shutdown | The boiler needs a pump overrun live and is wired only through the switched programmer circuit | Wire the permanent live and switched live exactly as the boiler handbook specifies for pump overrun. |
| The display flickers or the unit restarts at random | A loose L or N conductor, or the unit is not seated firmly on the wall-plate | Isolate the supply, retighten every wall-plate terminal and check that no conductor is held by its insulation. Refit the unit and tighten the securing screws fully. |
Frequently Asked Questions (FAQs)
Should I set the link to P or G?
Set the link to P if your heating and hot water are both pumped and each has its own motorized valve, so they can run independently. Set it to G if your hot water heats by gravity circulation. In G mode, hot water can run on its own, but heating cannot run without hot water. Most modern systems with a mid-position valve or two zone valves use P. If you are unsure, trace the cylinder pipework: no valve or pump on the cylinder circuit usually means gravity.
Does the LP722 need an earth connection?
No, the LP722 itself does not need an earth because it is double-insulated. The wall-plate still has an earth continuity (loop) terminal. Use it to join the incoming and outgoing earth conductors so the earth path to the boiler, pump and valves is unbroken. Never leave earth conductors cut back or disconnected inside the wall-plate just because the programmer doesn't use them.
Can I fit the LP722 onto my existing programmer's wall-plate?
Often you can, because the LP722 uses an industry-standard wall-plate. Many current programmers already use the same N, L, 1, 2, 3, 4 layout, and those can be swapped without touching the wiring. Older or other-brand units may number their terminals differently or need links, so compare the old model against Drayton's terminal comparison chart and rewire the plate if needed. Also check there is 70mm clearance on the right and 25mm above.
Are the LP722 outputs voltage-free?
No. On the LP722, L feeds both switch commons inside the unit, so terminals 1 to 4 output 230 V AC. That suits standard UK heating systems, where the programmer sends a 230 V call to the thermostats and valves. The Lifestyle timeswitches, such as the LP111 and LP711, have voltage-free contacts instead. If your boiler needs a voltage-free or low-voltage call, the LP722 is not the right control without an interface.
Can the LP722 power a pump or boiler directly?
Each switch is rated 2(1) A at 230 V AC: 2 A for resistive loads and 1 A for inductive loads such as motors. In a standard installation, the outputs only carry signals to the thermostats and valves, and the boiler and pump are switched through the junction box and valve auxiliary switches. Avoid running a pump straight off an output. If a load is larger than the rating, use a relay or the boiler's own controls.
What are the HW OFF and CH OFF terminals for?
Terminals 1 (HW OFF) and 2 (CH OFF) carry 230 V when that channel is switched off. Some systems need an "off" signal. A common example is a mid-position valve system, which uses the hot water off signal so the valve can move to the right position. In many two-valve systems these terminals are not used. Connect them only where your system's wiring layout shows a wire.
Is the wiring of the LP722Si the same as the LP722?
Yes. The LP722 and LP722Si share the same installation instructions, wall-plate, terminals and 230 V AC rating, so the wiring is identical. The Si version adds a service interrupter that warns when the boiler service is due and can later reduce heating to a safe but uncomfortable level. Setting up the service period needs the separate LPSi reset unit, not any extra wiring.
Will the LP722 lose its program in a power cut?
No, the program and the time are kept without mains power. During a power cut the display goes blank and the outputs stop, because the switches need the 230 V supply. When power returns, the programmer carries on with its set times. The clock is set at the factory and changes automatically between winter time and summer time, so you rarely need to adjust it.
Can I use the LP722 with a combination boiler?
You can, but a dual-channel programmer is usually more than a combi system needs, because a combi has no stored hot water channel. With only the heating channel wired, the HW terminals are simply left unused. Drayton recommends its single-channel timeswitches, the LP111 or LP711, for combi boilers. Check the boiler handbook for whether it expects a 230 V switched live or a voltage-free contact.
Can I mount the LP722 on a surface box?
No, a surface mounting box must not be used. Fix the wall-plate either directly to a flat wall with wall plugs and No. 6 x 1" screws, or onto a flush single conduit box type UA1 (BS4662) with M3.5 x 14 bolts. The surface behind it should cover the whole back of the unit. For surface wiring, snap out the cable entry strip on the bottom edge of the wall-plate.
