Pump only running when timer set to “on” rather than “timed”

[ceecjc1]

Hi heating experts!

The house is occasionally cold in the mornings and on investigation it looks like my central heating controller seems to not always be turning the pump on reliably when in 'TIMED' mode.

(Boiler is a Viessman Vitodens 100 and the pump is a Wilo variable speed pump all controlled by a Drayton LP522 controller).

The thermostat in the hall is calling for heat, the controller is set to 'TIMED' with both central heating and hot water switched on (both green lights are lit). The temperature of the water in the boiler is 23 degrees. The pump is not running (the light on the pump is off and water is not flowing).

When I manually cycle the controller from 'TIMED' to 'ON' the pump starts to run, the boiler fires up and everything heats up as expected. When I cycle the controller back from 'ON' to 'TIMED', even though both CH and HW are still enabled, the pump stops running and the boiler goes off. Note that at some point later the pump begins running again even in TIMED mode, so it's not a constant problem.

Is this a controller problem or is something else supposed to trigger the pump when i timed mode?

Thanks a lot!

Chris

 

[stem]

I suspect that as you have a Drayton LP522 controller that there is a hot water cylinder connected to the boiler and that the central heating and hot water are fitted with a single 3-Port motorised valve (aka Y-Plan) or, two 2-Port motorised valves (aka S-Plan) If so, the sole role of the Drayton LP522 and its associated room, and cylinder thermostats, is to open and close the valves. (it doesn't control the boiler and pump)

Inside the motorised valve/s is a small microswitch that when the valve winds fully open the switch operates and starts the boiler. I can't remember the pump configuration for your boiler. Usually, (but not always) the boiler controls the pump.

So, assuming that you do have motorised valves, the first check is to see if the central heating valve is opening, if it is, the LP522 is doing its job. If it not open, provided that the room thermostat is calling for heat the LP522 is probably at fault.

Usually with a temperamental fault it tends to be the microswitch and your giving the motorised valve a nudge by switching it from timed to on may just be enough to make the microswitch operate. Or, the valve may be stiff, or the motor weak. However when you say....

When I cycle the controller back from 'ON' to 'TIMED', even though both CH and HW are still enabled, the pump stops running and the boiler goes off

which I think is unlikely to happen.

If you are handy electrically. To test the wiring a simple move of the wire from LP522 terminal 4 to terminal 3, will allow the CH to be controlled by the HW channel. Obviously then both CH and HW would come on according the the set times for the HW. But if the fault remained then that would show it's not caused by the CH channel of the programmer, if the fault disappears it is.

If your set up is not a S-Plan or Y-Plan, then please provide details of your installation.

 

[Murdochcat]

What make and model controller do you have ?

And has it previously worked ok?

 

[ceecjc1]

Hi stem - thanks for the response and the details!

You are correct - there is a hot water cylinder and two 2-port motorised valves so this is S-plan.

I agree it seems odd that changing from ON to TIMED switches everything off since as far as the controller is concerned, ON and TIMED are the same thing during a timed-on period, but just to clarify, when the pump is stopped (when I think it should be on) I can cycle from TIMED to ON and everything fires up, then from ON to TIMED and everything switches off again, back to ON and it works, back to TIMED and it stops, quite reliably. (I haven't tried moving from TIMED to ON when the pump is already running).

So from what you're saying the boiler turns on when the water is cold and the valves are open, and the LP522 only controls the valves, so I should check the valves and see what's going on there - I can try to move the wire in the LP522 and see what happens. What's the best way to know if a valve is open or closed?

Thanks,
Chris

 

[ceecjc1]

What make and model controller do you have ?

And has it previously worked ok?

Hi Murdochcat

Drayton LP522. Yes it's been working ok for a long time. I've only recently noticed this problem in the last few weeks because the house has occasionally been a bit cold. Eventually the pump seems to kick in and the heating comes back on again, so it's been tricky to notice.

Come to think of it - the PCB in the boiler got replaced just before Christmas, not sure if this could somehow be related.

Chris

 

[oilhead]

If it all works on ON but not timed, then the valves are working. Check the timer outputs at the junction box, but I'm pretty sure the programmer is fluffed.

 

[stem]

What's the best way to know if a valve is open or closed?

When a valve is open, the manual opening lever at the base of the motor can be moved easily, it will feel 'loose and floppy'.

If the valve is closed when the lever is moved there will be some resistance as it winds the valve open, you may also hear a whirring noise.

 

[desktop987456]

Have you tried resetting the timer?
Is pump connected to pump port on pcb or in wiring center?
I have the same boiler and programmer. My pump is connected to one of the port on boiler PCB so it is getting power from boiler and it works fine in 'timed' or 'on' mode.

 

[ceecjc1]

Have you tried resetting the timer?
Is pump connected to pump port on pcb or in wiring center?
I have the same boiler and programmer. My pump is connected to one of the port on boiler PCB so it is getting power from boiler and it works fine in 'timed' or 'on' mode.

I haven't reset it yet, I can try this. The pump seems to be connected to a wiring center, there's a lot coming and going from it and I haven't opened it up and traced it. I assume the pump connects to the boiler from there.

 

[stem]

I haven't reset it yet, I can try this. The pump seems to be connected to a wiring center, there's a lot coming and going from it and I haven't opened it up and traced it. I assume the pump connects to the boiler from there.

With some installations, the pump and the boiler are simply wired together, so that when a motorised valve opens it starts them both, and when it closes they both stop. Other systems have a pump overrun. Here the motorised valve just starts the boiler and the boiler subsequently controls the pump via special 'pump' terminals to connect it to. This keeps the pump running for a few minutes to dissipate residual heat from the boiler.

 

[ceecjc1]

Thanks everyone for the inputs. I wanted to come back and post the solution.

It turns out the controller was not sending the 240V to the thermostat so it didn't know that the heating needed turned on. This must have been an intermittent fault in the controller (but I still don't know why this only occurred during 'TIMED' rather than 'ON'). Replacing the controller seems to have solved the problem.