Grant outdoor vortex pump overrun

[jeburf]

The boiler is heating the hot water and central heating fine but there is a problem with the pump over run. It seems to run for a totally random amount of time from about 10 minutes to overnight.

I think that the overrun on this boiler is controlled by an electrical timer than a thermostat, is this correct?

Is this a simple fix?

 

[Norcon]

Probably not overrun but a faulty programmer or zone valve.

 

[oilhead]

There is a frost stat fitted to this boiler. Is this overriding the unit?

 

[Boilerman2]

Only the GRANT COMBI PRO model has a pump over-run faciltiy

External boilers have a Frost stat which fires the burner nad runs the pump when it's chilly out

But I suspect you have a sticky auxilary switch on one of your Motorised valves - classic symptoms!

 

[jeburf]

Only the GRANT COMBI PRO model has a pump over-run faciltiy

External boilers have a Frost stat which fires the burner nad runs the pump when it's chilly out

But I suspect you have a sticky auxilary switch on one of your Motorised valves - classic symptoms!

Thank you.

Is there an easy way of testing for this or should I call someone out?

I am a very competent DIYer when I have a set of instructions to follow but too much of a wimp to poke around blindly!

 

[snb]

common problem when people fit external boilers and connect onto 3 port valves. should be fitted onto two 2 port valves and have an auto bypass.

then when the frost stat calls it only pumps heat around the index circuit and the hot water or the heating.

 

[jeburf]

By motorised valve, I assume you mean one of these:

If so, I don't seem to have one. Pictures of my boiler below:

Untitled

• jeburf
• 29 Dec 2012
• 1

Untitled

• jeburf
• 29 Dec 2012
• 1

How does a frost stat replace the need for a pump overrun? I thought a pump overrun was used to cool residual heat in the boiler and the frost stat used to prevent things freezing in the cold.

 

[jeburf]

bump

 

[oilhead]

Frost stat does not replace pump overrun. It runs the pump in cold weather to stop freezing.

 

[Norcon]

Ooh dear. A combination boiler.
Wouldn't take the gift of that heap of junk. I'd light an open fire and swing a cauldron above it first.
Probably cost you a small fortune too!

 

[oilhead]

Do you realise if you have the hot water on permanently that the boiler will fire up to maintain the heatstore temperature at random intervals?

 

[jeburf]

Do you realise if you have the hot water on permanently that the boiler will fire up to maintain the heatstore temperature at random intervals?

I do. The problem is that the pump continues for an excessive amount of time once the burner shuts down

 

[oilhead]

Which pump runs? CH or DHW?

 

[jeburf]

DHW I think, the green one in the bottom right of the second picture