tank overflowing pump constantly running

[flinty]

I have a system that has a pump for the central heating and also another grundfos pump built into the hot water side of the system.
The tank is a two part one with hot water below and I presume the f&e tank above.
The hot water must be linked to the mains as there is no header tank to feed the hot and the flow stops when the mains supply is turned off.

The problem seems to be that the hot water pump is constantly running and seems to be slowly filling the tank above it which is then flowing out through the overflow.
It's definitely not the filler for the upper tank as I have turned that off.
Any help would be much appreciated.

 

[tripty]

Sounds like you have a fortic cylinder, could you take a pic? What pumps do you have? Is the one on the hot water a Grundfos 15-90?

 

[matt1e]

or a pulsacoil or other type of thermal store

 

[flinty]

the pump on the hot water side is a grundfos 15-50 and the c/h one is a grundfos 15-60.
the therory that I have is that there is a small rupture in the heating coil inside the tank and the pump thinks water is being drawn off and is pumping as a result.
Does this sound feasible?

[/img]

 

[tripty]

Hi,

Are you sure one pump is on the domestic hot water (dhw)?

From your pic I think you have a thermal store, therefore the 15-50 won't be on the dhw as you would have mains dhw. One pump will be to the boiler (you do have a boiler ) and the other to the rads. Thats my guest

Your right it that you've probably got a split coil, if so your cylinder is f*cked

 

[Andygasman2010]

It's difficult to know why the pump is running all the time without knowing a bit more about the system, some thermal stores say the boiler/pump should be on 24hrs anyway so it might be normal. The overflowing problem is like you said, a split coil meaning mains water is filling the cylinder. New cylinder needed by the sounds of it!

The top connection to the coil has no bleed point on it so it looks like it's a direct cylinder and doesn't actually have a coil to heat it up. Is the cylinder the highest point on the system?

 

[flinty]

yes it is the highest point in the system.

 

[Andygasman2010]

I wouldn't worry about the pump issue, at least until you change the cylinder which is what's causing the overflow.

 

[flinty]

Going to change the whole system over to a combi I think. Having had a quote for a new cylinder it seems stupid when it will still leave a 15 year old boiler in place.
cheers for the help.

 

[Andygasman2010]

That cylinder will probs give about 20 litres per min of hot water, you'd need a pretty big combi to equal it! What did you have in mind?

How many baths/showers do you currently have running off that cylinder?

 

[flinty]

probably go for a 33 kw baxi duotech.
Just the one bath and shower so it's more than enough.