Vaillant 630, megaflo + nest

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Hello,

I know this topic comes up a lot so apologies!

We have just moved into a new house that has a Vaillant boiler, megaflo and a nest 3 thermostat installed.

It is my understanding that the boiler always needs to be ‘on’ for the hot water to work, and then the radiators are controlled by the thermostat. When we turn off the heating on the Nest, the heatlink clicks but the radiators stay on. Is the hot water also controlled by the Nest?

i have a picture of the heatlink wiring which I’ve attached.

Our sellers left us no instructions for how to use anything in the house so scrambling around trying to make sense of everything so thanks for your help!
 

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your Nest controls 2 x zone valves one for heating one for HW theses valves tell the boiler when to come on, it sounds like the CH zone valve is faulty
 
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Hi Ian - thank you for this!

Would this be in the heatlink, or an issue with the boiler itself?

Thanks!
 
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no on the zone valve itself, you have 2 probly in the airing cupboard where the mega flow is but not always , post a pic of the megalo and connected pipes and we will tell you how to chjeck them
 
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Hi Ian,

The megaflo is the loft, the boiler is in the kitchen if this makes any difference.

Attached are some images of the megaflo
 

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nope your valves are not shown there, you have what is called an S plan so you will have two valves some examples of what you are looking for


Different brands have different actuator heads but all do the same thing, yours might be plastic and different colours there are many variants
 
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CBW

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You’re looking for something similar to this:

1658934709293.jpeg

so should be in vicinity of the megaflow or what would have been the airing cupboard.
 
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There is nothing like that near the megaflo, just multiple pipes. I’ve attached the boiler set up from the kitchen. Not sure if they makes it any clearer?
Lesson learnt - make sure sellers leave a handover document!!

Edited to add -realized it must be those two silver Honeywell boxes - is there anything I can check or is this one for the professionals :D
 

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CBW

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The x2 metal ones with black cables and yellow/black warning sticker - they’re the zone valves.
 
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we have got there eventually what you call honeywell boxes are the zone valves, you will see a small lever on each valve, when the valve is working correctly and doesnt have a demand for heat, when you try to move that leaver manuslly you should feel a resistance, if the actuator or valve is faulty the lever will offer no resistance when you try to move it into the manual position, switch the CH and HW both to off and feel the manual levers on each valve , they should both offer resistance when you try to slide them across, betting the CH one doesnt
 
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Hi Ian - you are right, unfortunately :D could move one side with zero resistance!

now for the fix.. can it be done by me or is that something I get a plumber/electrican in for?

Thanks
 

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Hi Ian - you are right, unfortunately :D could move one side with zero resistance!

now for the fix.. can it be done by me or is that something I get a plumber/electrican in for?

Thanks
Depends on your diy capabilities, but we can offer assistance on here if needed. It’s likely to be the actuator (the head part).
 
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Hi Ian - you are right, unfortunately :D could move one side with zero resistance!

now for the fix.. can it be done by me or is that something I get a plumber/electrican in for?

Thanks
nothing to stop you doing it yourself, legally if you are happy to tackle it, your valves have the little dimples on tham so means you can swap the actuators with out any draining, there are many videos on youtube showing you what is involved, I would however recommend using one of these for all they cost they make things so much easier, I use them every time, and if you ever need to swap the actuator again in the future makes life very simple, it might just be the synchron motor that has seized, but that is a harder job to swap out although cheaper, all depends on what you are comfortable in doing.


If you are not comfortable doing it yourself it is bread and butter stuff to some of us so if you say what area you are in we might know someone near you that we could recommend
 
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Thank you so much for helping me to diagnose - turns out my husband's dad has just done this in his own house (he is very competent at DIY!) so already has the part on order for us and is coming round to fix

Thanks again for your help, it was invaluable!
 

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