Central Heating Pump Runs For Long Periods of Time

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Hello Everyone,

I am a newbie to the forum and I have reviewed several posts on the forum about central heating pumps running continuously. My problem is slightly different as my central heating circulation pump run intermittently for hours.

The system configuration is as follows:
Vaillant EcoTec Plus 435 condensing boiler (the DHW is set to off on the boiler)
Vaillant VR66 Control Centre (with E-Bus)
Vaillant V-Smart wireless room thermostat
S type system configuration for DHW and central heating.
Hot water cylinder with immersion heater connected to a 230V wall switch and a Honeywell L641A1005 cylinder thermostat.
Honeywell V4043H1106 zone valves (x2) (One for DHW and one for central heating)
Boiler pump over run is set to 20 minutes.

During the day when the central heating is running the DHW zone valve remains off and only the central heating zone valve opens when the room thermostat calls for heat. However, at night when the room thermostat is set to 10 degrees Celsius (typical night time setting for my home), the DHW zone valve energises (at some point during the evening) and the circulation pump runs constantly (even though the DHW is set to off on the boiler). I believe Vaillant boilers have default DHW priority heating but if the DHW is set to off on the boiler, I do not understand why the DHW zone valve is energised and the circulation pump runs constantly. The pump over run is set to 20 minutes but the circulation pump runs for hours.

The same problem occurred with the previous Baxi condensing boiler system. Therefore, I believe one of the other components in the in the central heating or DHW system is causing the problem. I noticed in VR66 Control Centre manual advises the DHW cylinder thermostat should be normally open. I inspected the configurate of the Honeywell cylinder thermostat and is currently configured in the normally closed position. However, I have tried disconnecting the cylinder thermostat from the VR66 control centre but the DHW zone valve still opens intermittently at night and the circulation pump runs for hours.

I would appreciate any guidance on what could be the cause of this fault.
 
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As configured now, with cylinder stat wired NO, if the CH is programmed off and you initiate a call for HW by turning the cylinder stat up what happens?, does the cyl zone valve open and the boiler fire up?
 
Thanks for the suggestion. I will configure the cylinder thermostat for normally open and run the system overnight. I will report back with the result.
 
I should add the cylinder thermostat is currently wired in the normally closed configuration.
 
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I should add the cylinder thermostat is currently wired in the normally closed configuration.
Normally, I think a cylinder stat in S system has only one set of contacts with live to the common C and 1 to the boiler and/or zone valve, you could use a cylinder stat with two sets of contacts like used in a Y system where you have C, 1 and 2, terminal 2, C & 1 should be used so that the 1 opens when the stat is satisfied, if C & 2 are used then 2 will close when the stat is satisfied, but couldn't work in a heating application?.
 

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Normally, I think a cylinder stat in S system has only one set of contacts with live to the common C and 1 to the boiler and/or zone valve, you could use a cylinder stat with two sets of contacts like used in a Y system where you have C, 1 and 2, terminal 2, C & 1 should be used so that the 1 opens when the stat is satisfied, if C & 2 are used then 2 will close when the stat is satisfied, but couldn't work in a heating application?.
Cheers. I just purchased a Honeywell L641A1039 cylinder thermostat with both S and Y system configuration options. I will wire the new thermostat as normally open and give the system a trial overnight.
 
Sorry for the late update. I wired the new cylinder thermostat (Honeywell L641A1039) in the normally opened position using contacts C and 2. When the DHW was turned on at the boiler, the DHW zone valve did not energise and the boiler did not fire.

I decided to leave cylinder thermostat wired in the NO position overnight. As usual (at some point during the evening) the DHW zone valve energised and the central heating pump ran for hours. The DHW was turned off at the boiler.

The next morning I rewired the cylinder thermostat in the NC position. With the new cylinder thermostat wired in the normally closed position, the DHW zone valve did energise and the boiler did fire (when the DHW was switched on at the boiler).

Upon further investigation I discovered that levers (for the zone valve microswitches) do not make contact with the microswitches in either zone valve. The current wiring bypasses the integration of zone valve microswitches with the central heating pump circuit (not good) as the microswitches never change state. I have decided to replace both zone valves and trace the wiring to ensure the new zone valve microswitches are integrated into the central heating pump circuit. I will then monitor DHW zone valve to see if it energises overnight with the DHW switched off at the boiler.

I will keep you updated on the outcome.
 
The cylinderstat should be wired, permanent live to C and switched live to 1, period. Normally this switched live commands the cylinder motorised valve to open, the auxiliary set of contacts in the motorised valve then commands the boiler to fire up, on modern boilers the boiler then controls the pump, start, stop, overrun, anticycle time etc.
 
Many thanks for the wiring advice.

The VR66 Controller has direct connections for the thermostat, central heating pump, DHW zone valve E Bus and the central heating zone valve. I have attached a couple of photos of the controller wiring. This appears to suggest the controller is managing the switching without the use of the zone valve microswitch interlocks (please correct me if I am wrong)

I also have to make a few corrections from my previous text. Upon further investigation I realised the zone valve microswitches did not make when I opened the valves manually but they did switch state when the zone valves were energised. I also ohmed the microswitches in both zone valves and both are working properly. Also the zone valve motors are working properly.
Currently, none of the zone valve microswitch wires are connected (e.g. white, orange and gray wires are not connected) all switching occurs through the VR66 controller.

I had time to observe the system fault today and I discovered the scenario which causes the DHW zone valve to open (even when the DHW is turned off at the boiler).

I set the boiler flow temperature 45 degrees and turned the DHW off at the boiler. The room thermostat was set to 25 degrees (which was above the 20 degree ambient temperature in the room) The boiler fired to drive the flow temperature to 45 degrees and switched to standby mode when the flow temperature on the boiler display reached approximately 50 degrees and the ambient room temperature reached 25 degrees. The DHW zone valve remained de-energised while the boiler fired to reach the set room temperature. I returned the room thermostat to 20 degrees after the boiler went into standby. The boiler remained in standby and the both zone vales and the central heating pump remained de-energised until the flow temperature dropped to approximately 44 degrees. At this point both zone valves opened and the central heating pump began to run but the boiler did not fire. The system remained in this state for over an hour with no change. The ambient room temperature was approximately 22 degrees. When I set the room thermostat to 25 degrees ( 3 degrees above ambient room temperature) the boiler fired and the DHW zone valve de-energised. Once the flow temperature was above 45 degrees I lowered the room thermostat to 20 degrees and the boiler went into standby. The central heating zone valve de-energised and the central heating pump switched off.

The problem appears to be when room stat holds the boiler off but the boiler wants to fire to meet the set flow temperature. The system seems to glitch causing the zone valves to energise and the central heating pump to run indefinitely. As soon as the room stat is increased to a temperature where the boiler fires, the DHW zone valve de-energises and once the set room stat temperature and flow temperature is reached, the boiler goes into standby and the central heating zone valve and pump are de-energised.

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