vaillant 838 ecotec heating restarts when hot water turns off

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So weird one maybe. I have just been watching my boiler (I know its a slow day) and I set my flat for heat demand and my wife was in the kitchen. watching the start up sequence for heating and all is going well, then wife opens tap and hot water demand comes on screen. all good. she closed the tap. and boiler looks like it shut everything down.
it says DHW mode pump overrun. then that eventually goes off screen and it says heating mode start. and the cycle starts again.

I tried 3 or 4 times with the local tap and yep. it appears to me the heating mode stops when I close the hot water demand.

any idea, do I need to get my plumber in?
 
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Isn't hot water prioritised? Else you wouldn't get any with the heat on. I'm no expert though...
 
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so are you saying the boiler can only do 1 thing at a time? dunno why I just assumed it would run heating and manage hotwater along side.
 

CBW

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so are you saying the boiler can only do 1 thing at a time? dunno why I just assumed it would run heating and manage hotwater along side.
Yes, that’s how all combi boilers work. If you had a hot water cylinder, then yes it could send the water to both circuits.
 
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Yes, that’s how all combi boilers work. If you had a hot water cylinder, the yes it could send the water to both circuits.

Depending on the type of control system. Using Vaillant controls, it would only do one or the other, simply because the temperatures for each are different.
 
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New one on me (n)

Well I can assure you it is correct. Prior to installing the Vaillant control system, I had the Vaillant boiler on a basic wireless room stat, cylinder stat and a 3-port mid position. The boiler was limited to the setting of only one output temperature for both.

I soon swapped the basic controls, to the better more capable Vaillant ones, at which point the boiler allowed separate temperature settings for CH from the HW, but it also lost the ability to heat both simultaneously, the 3-port no longer used the mid-position. If there is a demand for water heating, the CH goes off until the HW demand is satisfied.
 
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Well I can assure you it is correct. Prior to installing the Vaillant control system, I had the Vaillant boiler on a basic wireless room stat, cylinder stat and a 3-port mid position. The boiler was limited to the setting of only one output temperature for both.

I soon swapped the basic controls, to the better more capable Vaillant ones, at which point the boiler allowed separate temperature settings for CH from the HW, but it also lost the ability to heat both simultaneously, the 3-port no longer used the mid-position. If there is a demand for water heating, the CH goes off until the HW demand is satisfied.

Yea, but this thread is regarding a Combi boiler.


so are you saying the boiler can only do 1 thing at a time? dunno why I just assumed it would run heating and manage hotwater along side.
All combi boilers only do heating or DHW, but not both at the same time. Doesnt mater who makes it or what controls you use.
 
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Yea, but this thread is regarding a Combi boiler.



All combi boilers only do heating or DHW, but not both at the same time. Doesnt mater who makes it or what controls you use.

Did you miss the thread going off at a tangent, when CBW mentioned cylinders?
 

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Did you miss the thread going off at a tangent, when CBW mentioned cylinders?
Wasn’t really off tangent, more just explaining the difference between Combi and traditional systems, as OP thought the Combi was capable of doing heating and hot water together.
 
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