Gas boiler continuous heating issue

[Jad30]

My gas boiler, a Vaillant ecoTEC plus 415 is doing rather odd and random things.

Everytime the boiler is heating hot water for the hot water tank (unvented cylinder) when it finishes the pump continues and pumps the rest of the water around the radiators making the house warm, there is no call for any heating. This lasts for approximately 10 minutes. At that point the pump goes off.

The Thermostat is a wireless type (Drayton) and the receiver does not indicate a heat when the pump is going.

Pump is a Grundfos Alpha2. 3 port valve is a Drayton.

Approximately once a week the boiler and the pump do their own thing they both come on and start heating the radiators. It's almost like the boiler is stuck in some kind of cycling mode, the timer controllers have no effect.

The only way I can reset this is to turn the boiler off for approximately 8 hours. It will then follow the timer settings of not needing to be on for a while before starting to play up again.

This appears to be a recurring cycle I'm into the second week.

Any ideas please.

 

[terryplumb]

What programmer do you have ? When domestic hot water only is selected to heat the cylinder do any radiators heat up at all ,or only after the cylinder is satisfied ?
Was the system working well ,and this problem recently arisen ?

 

[Jad30]

Programmer is a Drayton MITimer 1720R (7 day hot water and heating).

When it's heating only water none of the radiators come on, until the timer finishes its programmed cycle. Then the pump is still going and the radiators get warm. The system has been working fine for the past 8 years.