Vaillant Ecotec 630 - Pump Running Always

Hello all,

I have a 4 year old Vaillant Ecotec 630 boiler which is connected to a megaflo.

Both have operated without issue since new until, that is, last weekend.  At this time of year (summerimte) I run a HW cycle for an hour every morning between 5-6am. The heating hasn't been used since March.

Last weekend the HW cycle kicked in and heated the water in the megaflo during the prescribed programme. However, the pump continued to run and would not switch off.

I power cycled everything and when I switched the boiler back on the pump started running again.  I tried swithing the heating and HW on and off and whilst the boiler does fire and then stops, the pump is continually running.

I replaced the PCB and switched the boiler on and again the pump automatically kicks in and starts running again.

I don't know what to look at next. Can someone offer some advice?

Thanks.

 

Am I correct in my understanding that the thermistors are responsible for monitoring the temperature on the CH flow and return?

From what I can see they are fairly low cost items so I can change these for about £10. Cheaper than calling Vaillant.

 

I have replaced both thermistors and still have the problem.

When the boiler is powered up and the boiler thermostat turned up the pump and burner will fire. When the thermostat is turned down the burner will cut out but the pump will continue running indefinately, there is also a fan running too.

Vaillant want £285 plus VAT to visit.

Does this sound like it might be the pump which is at fault?

 

Managed to get BG out to take a look. His first recommendation was that it needed a new PCB. I told him that one was fitted 2 weeks ago.

He then made a call to his colleague and suggested that the system was wired incorrectly. To fix this it would be 2.5hours works at £95ph +VAT. I asked why he thinks it needs to be rewired given that it has worked for over 4 years. He said that when the heat dial on the boiler was turned up, the boiler would fire up and when it was turned down, then the heater would switch off but the pump would continue runing until it reached a cooler temperature. He said that the boiler shouldn't be operating in this manner as it is controlled externally via a programmer and thermostat.

If this is true then it has been running like this for 4 years and everytime the boiler was used, the pump would have taken ages to shut off given that when the heating or hot water thermostats are satisifed then it would only be able to cool down via the by pass circuit.

I can follow wiring diagrams so I wanted to check this is wired correctly before taking the next course of action. Does anyone have a diagram to follow where the system has a megaflo and a wireless room stat installed?

 

I have given this problem some more thought and ran through a wiring diagram that I found on S Plan layout.

As far as I can tell the wiring is correct. The problem seems to be with the control knob on the boiler itself.  If the programmer is off for both CH and HW and I turn the knob on the boiler to 60C then the pic of the rad will appear and the boiler will fire up.  It's as if the boiler is ignoring the external controls.

I've checked the wiring at the boiler too and in particular terminals 3 and 4. These are wired to the grey and orange wires of the 2 port pumps, they are also live - 240v.

I think today I have tired everything I can think of. I guess I am going to have to call in Vaillant and see if they can fix it but just before I do, anything I may have over looked.

 

Thanks that was the problem.  The motorised valve on the HW circuit was faulty. I had a spare one so all I had to do was remove the head and rewire. Everything working as normal now. Many thanks for all the input and especially to davy_gas who was spot on with the analysis!