Central heating pump overrun

[PatPower1]

Hi, I have a Vaillant EcoTec boiler which does the central heating and heats up our hot water in a cylinder as well.

We have just started to use the hot water on its own but have noticed the following:

(i) The water in the cylinder is heated up pretty quickly, and the boiler burner shuts off. However the pump just keeps on going and going. Is this normal?

(ii) With the hot water and central heating on the system is really quiet. However with only the hot water on there are loud rushing and banging sounds

Any clues? Would be most grateful

cheers pat

 

[D_Hailsham]

How many motorized valves do you have? They will probably be near your hot water cylinder. There will either be one, as in the left pic; or two, as in the right pic.

View media item 5946 View media item 11762

 

[PatPower1]

Hi thanks

I have two sets of valves. How do these cause the problem described?

Cheers Pat

 

[Ronald0]

Many boilers incorporate a pump over-run facility. Pump should run for about 10 mins.

Audible water movement is due to air in the system. Have you bled the primary hot water circuit? Is there an upstand valve on the flow to the heating coil?

Banging in the pipework is usually steam from boiling water as it exits via the vent pipe.

 

[D_Hailsham]

I have two sets of valves. How do these cause the problem described?

As RonaldO says, many boiler have pump over run, the purpose of this is to prevent a heat build up when it stops working. Obviously there must be somewhere for the water to circulate.

With two valves, as in your system, when both valves close because the CH and HW are up to temperature, there is nowhere for the water to circulate. This will cause noise in the system and can cause pump damage.

The solution is to have a bypass circuit, which is a pipe connecting the flow to the return immediately after the pump. This is fitted with a valve which restricts the flow through the bypass, although nowadays it is an automatic valve which only opens when the HW and CH valves have closed.

Many boiler have the bypass valve built into them. Which boiler do you have (make and exact model)?

 

[PatPower1]

Hi it is a Vaillant Ecotec Plus. I have also noted that the hot water from the boiler goes into the bottom of the cylinder and out the side further up - from the diagrams I have seen it seems to be usually the other way round. Does this matter, and could it be a contributory factor?

Cheers Pat

 

[PatPower1]

Ps and i have bled the air out as well. Not much of it. Still same banging problems. cheers Pat

 

[simond]

If you have an ecoTEC 6 series there is an internal bypass.

If you have a 4 series, the bypass must be fitted by the installer.

If the noise is only on hw, then chances are you have either a partial blockage or an airlock.

If you have an ecoTEC 4 series the pump will be external, and it could be wired incorrectly as this is done by the installer.

 

[PatPower1]

Thanks, I have checked, it is a 6 series.

If the boiler is on hw only, does it send the water round the shorter circuit with the same force as if the the ch and hw were on together. I was thinking maybe this is the problem - ie that there is just too much pressure in a smaller space?


Now my immersion heater has packed up as well. It is a never ending story.

Cheers Pat

 

[simond]

When the pump 'carries on forever', is the 'radiator' symbol in the LCD display illuminated or flashing?

 

[PatPower1]

hi Simon

That symbol is flashing on and off. Cheers pat

 

[simond]

That means your wiring is still asking the boiler to come on, but the boiler has reached its own internal limit temperature and running the pump to cool down.

So the problem is in your controls, Pat, not the boiler.

PS: You aren't the Westmead Pat Power?

 

[PatPower1]

Hi Simon

Thanks for your advice. Very helpful. Sorry not Westmead Pat Power - South Woodford Pat Power.

Cheers Pat