Vaillent 831 running cool

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Hi there.

I have an 8 year old Vaillent 831 with VRC430 weather compensator, which has been running well up until this cold snap. It's been completely reliable until this summer when the main board went and was replaced.

With the sudden drop of temperature this week, it became obvious that the rads aren't getting hot enough to warm the house properly and looking at it, the boiler is only getting up to 44 0c. The heating curve is set to the same as it has been for 8 years and the outside temperature being displayed is accurate. Winding the thermostat up to 30 and the heating curve up to 3 still only gets the boiler up to 47 degrees. Hot water is still fine, so it doesn't seem to be a mechanical problem stopping it getting above this temp.

It doesn't bring up any fault codes.

Any ideas much appreciated!

Barry
 
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Does the temp increase/decrease on display when altering central heating temp dial?
Could be broken dial spindle.
 
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It makes no difference I'm afraid. It's set to maximum all the time with the weather compensator fitted, which I think effectively by passes it. As I said, it will fire at full bore for hot water, so it's something on the central heating side I'm sure.
 
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Might be worth going through the boiler parameters to see if anything like "max temperature" has been changed. Should be in the installation guide.
 
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I don't think the WC bypasses the Heating temp spindle.

You should leave it at 100%.... but if you've had the board replaced there's every chance the spindle has snapped. Easy enough to check by turning the knob and looking at the back of the board to see potentiometer moving..... of course you'd have to get a gas safe man to remove and replace cover......
 
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As above, but if you turn the ch knob down a little then back up and the spindle is ok, you should see the display temp rising to high 70s/80 degrees
 
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Thanks all, it's now fixed! Armed with my nice new glasses, I realised the square rod was in the potentiometer 90 degrees out, so max was in fact only 3/4 of max. Just didn't come to light until it was cold enough to need more than 3/4 heat.
 

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