Pump wont stop after hot waters turned on

[HowDoISort]

I wondered if anyone could help please. A friends water pump keeps running forever.

I don't have every detail about his setup, but know the following:
Its not a combi boiler, but an older-style hot water tank.
His wiring centre is branded Danfoss, as are the two motorised valve heads (one for heating one for hot water).
I believe the programmer's a Danfoss FP715SI, but arent 100% certain of the model.
Both the heating and hot water do get hot.
If the mains supply to all of it's turned off/on, the pump behaves normally as the central heatings turned on/off, but once the hot water's turned on the pump starts and never stops.
The boiler stops when the water's hot, it doesnt keep running forever.
I'm not sure if its useful without a lot of labelling, but his wiring centre looks like:

He thinks the problem started after his boiler was moved ages ago, but isn't 100% certain.
The water tank thermostat's been swapped and made no difference.

Neither of us are plumbers or sparkies, but we're both pretty practical. Just not familiar with central heating systems. We've got basic tools inc a multimeter.

Hows it best to approach it to figure out the cause?
Huge thanks in advance.

 

[Exedon]

What your describing is known as 'S' plan
Lots of wiring diagrams on line .
My first suspected would be hot water zone valve .
Honeywell do a decent app that you can download to your phone that includes a trouble shooting section and clear Wiring diagrams
Wiring colours identical on the Danfoss valves .

 

[HowDoISort]

What your describing is known as 'S' plan
Lots of wiring diagrams on line .
My first suspected would be hot water zone valve .
Honeywell do a decent app that you can download to your phone that includes a trouble shooting section and clear Wiring diagrams
Wiring colours identical on the Danfoss valves .

Thanks a lot
The hot water is getting hot, which I guess means the motor/valve are probably ok?
I've had a search and found a video of someone pulling the valve head apart, would the microswitch in there be a likely culprit?
If not that, then we should check how things are connected between the tank thermostat, programmer and wiring centre?

 

[terryplumb]

When hot water only is on and it heats water are you certain the boiler closes down? Could it be still running but very intermittently and just not noticed ?

 

[HowDoISort]

Would that mean the water in the tank would always be hot? It sounds like that isn't the case.
We should be able to double-check tomorrow.
He has mentioned the floor in his bathroom's always warm (and maybe the radiator but I'm not sure). Would that be a heatsink for the system, that would make sense if the boiler's always running?

When only the hot water's turned on, what is it that should stop the pump running?
Is it the thermostat, and then any run-on control the boiler does?
I'm not sure what boiler he's got, or if it does anything like run-on (do some not?)

 

[terryplumb]

The motorised valve sends voltage to the boiler to fire it up ,the boiler should send voltage to the pump therefore controlling it, when demand for hot water is satisfied / ceases the boiler will close down and it should control how much longer the pump runs to dissipate any heat within the boiler.
Your system may not be wired this way,you would need to do some testing to establish where the voltage is coming from to keep the pump running continuously.

 

[ericmark]

I will guess the micro switch in one of the motorised valves has stuck?

If not fixed, it can mess up the pump. Often remove the head, and give it a tap, and the switch starts to work again.

 

[HowDoISort]

Had a look yesterday and we're pretty sure we're on the right track.
The boiler was running all the time the pump was.

Had the valve head apart and checked continuity through the switch while pressing it repeatedly. It was inconsistent/sticking.
Gave the switch a few sharp taps and put it back together. Turned the water on/off a few times and everything did what it should twice, but on the third go the pump and boiler didn’t stop.

A couple of new switches are on the way to his and we'll swap one (or probably both) in a few days.

Thanks for your help, just knowing we weren’t miles off the mark was great.