Pump overrun/bypass question.

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I have Vaillant Ecotec plus 418 heat only boiler. It’s fitted in the loft. The pump and bypass are in the downstairs airing cupboard so approx 10m flow/return combined run. I’ve just lagged all my pipes so the only uninsulated section is approx 2m in the airing cupboard. I know the factory standard overrun time is 5 minutes and I’m wondering if that now the pipes are insulated, will 5 minutes be enough to dissipate enough residual heat before shutting down? Is there a way to test this - is there a preferred temperature I need to get down to before allowing the pump to shut off?
 
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Does the boiler not go into anti cycle mode if the pump overrun is not sufficient?
 
I'm sorry, I don't know what that means! How can you tell when that is happening?
 
There was a thread on this recently. Search for posts by me.

I think s8 was anti cycle, s7 was pump overrun.
 
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I'm interested in what you find out here, Motman...

I have the 418 and I think the flashing rad symbol on the display indicates anti-cycling. Also the s8 as fezster said (you need to press 'i' to see the status display).

I find mine goes into anti cycle every time it switches off; but if yours only anti-cycles with your pipes insulated, that solves my own mystery!
 
My rad symbol is solid but flashes when its heating up. I think that signifies that the room stat or hot water cylinder is calling for heat. I suppose if its going on and off each time the heating and hot water are on and not tripping anything out it should be okay. I just wondered whether any long term damage could occur if the returning water is not quite cool enough. I was thinking that If I could find out what the 'safe' temperature was, I could set the overrun to maximum, let the system heat up, switch the room stat down and time how long it takes for the bypass to reach a safe temperature and then reset the overrun to that time. Or am I overcomplicating things here?
 
I don't know the answer, but I think the purpose of the bypass is just to remove excess heat from the exchanger in the boiler...
As long as you observe the temperature stabilizing during the pump overrun you should be ok. I can't imagine the boiler will be damaged by hot water sitting in it as long as it's not getting hotter.

With my setup (and I know my bypass is too short), I observe the temperature reducing immediately after the bypass valve opens (presumably as the cooler bypass water goes thru)... then increasing (presumably as the bypass loop heats up from the residual exchanger heat), but not as high as flow was... and then gradually reducing to mid 40ies.
So my bypass only manages to lose 10C.
 
The Bypass isnt there to loose heat, its to maintain flow throught the boiler and on pump overrun to allow the flow and return temperatures to equalise. You'll be fine with them lagged
 

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