Pump not switching off ?

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If anyone can provide advice please,

We have an oil fired Potterton Statesman 70/90L boiler which along with a Danfoss Alpha pump, Drayton Digistat Thermostat, Digistat SCR wireless system, Drayton Lifestyle Timeswitch and two Drayton ZA5 acuator valves - all were fitted in 2005 - so now 12 years old.

I did change one of the click on acuators myself when it failed some three years ago.

The boiler has been serviced regularly each year and apart from the above the system has worked faultlessly.

In last couple of days the Danfoss Alpha pump has been staying on after the timeswitch has turned off the boiler. In this condition the acuator valves have both been turned to closed position and if the heating switch is pressed to call for heating the actuator valve moves to the open position - the hot water one opens too if that switch is pressed.

Both acuator valves close if the switches are pressed to off and the boiler switches off - - the pump however continues to run and the only way to switch it off is by turning off the electric supply to the system.

Advice on what is wrong please.

David.
 
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Pump should turn off if the boiler does as both are supplied from the same source. ie Zone valve orange wires
 
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Thank you.

Does that mean the electric supply from the actuator zone valve to the pump is staying live for some reason - whilst the supply to the boiler is switching off as it should ?

Is it something I can check with a multimeter and how do I do it ?

David.
 
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They should both be wired to the same connection, As in Honeywell S plan.
If the burner is off...the pump should also be.
Where is the pump connected to ?
 
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The pump has one cable - to a mains point on the wall.

This mains point has a cable from it to a junction box further up the wall.

The junction box also has cables from both zone valves, the wireless controller and timeswitch going to it - so without taking the cover off the mains point or junction box - I would say the pump is connected to the mains point then onto the junction box to join up with all the other parts of the system.

Does that sound right ?

David.
 
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Your description of various points boxes and cables tells me nothing.

Take the Fookin lids off !!!!ISOLATED and post a photo or accurate sketch.
 
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if you are happy that the zone valves move freely and are not sticking open, it is usually the micro switch in the zone valve head that is not turning off when the valve closes. With controller off and pump still running, check the orange wires in the junction box for 240v (between orange and neutral). If voltage there, carefully remove orange wires and check individually. Trace the one with voltage back to its head, i.e. Heating or hot water. That is the culprit. Normally just replace the head.
 
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if you are happy that the zone valves move freely and are not sticking open, it is usually the micro switch in the zone valve head that is not turning off when the valve closes. With controller off and pump still running, check the orange wires in the junction box for 240v (between orange and neutral). If voltage there, carefully remove orange wires and check individually. Trace the one with voltage back to its head, i.e. Heating or hot water. That is the culprit. Normally just replace the head.
If a micro switch was sticking then the boiler would keep firing too not just the pump
 
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your pump is wired into the boiler controls and if the recommended pump overrun has been installed that will be where you should look.
 
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Ian,

Thank you - - - I've investigated the boiler details and there is a pump overrun thermostat built into it.

Is that what I should look at ?

David.
 
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David, when your boiler is asked to shut down by the programmer or room thermostat or whatever there is still a lot of heat within the boiler, the pump over run keeps the pump running to dissipate this heat and protect the boiler, it sounds like this is faulty , some are set by a timer most have a sensor that tells the pump over run when the boiler is cool enough to turn the pump off, it sounds like there is a fault with yours
 
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Ian,

Thank you for providing precise advice that this amateur can understand - it looks like the overrun sensor is the culprit.

David.
 
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