problem with CH makeup tank getting hot

[calibra]

I believe mycentral heating was fine before I had my extension built, it is a fuly pumped system with ahot water cylinder etc.
During the extension I have had several rooms added and the rads have about doubled, using same boiler ( potterton neataheat ) and pump.

When the CH pump is on low or medium speed everything is ok.

When I increase the speed to maximum, the makeup tank gets very hot and there is often a flow of very hot water returning through the expansion pipe.

My first thought was to raise the return pipe ( 1metre possible) to give extra `head` and hopefully stop the hot water eturn. Turning down the boiler temperature seems to have no effect.

I have just fitted a temporary hose which raises the return pipe by about 1 metre to see if this helps with the CH pump on full speed

Thanks

Calibra

 

[Agile]

If the system is properly balanced then the pump should work perfectly OK on the "2" setting.

It sounds as if the system needs balancing and is also rather blocked around the point the cold feed joins the system.

You dont need to do anything for the time being as long as you dont let it pump over. The vent should go at least 450 mm above the water level in the F&E tank. You can raise it further if that helps but it does indicate a blockage or wrong pipework layout.

Tony

 

[calibra]

I don`t believe any pipework is blocked, I have flushed the whole system and refilled with protector chemical. It all drained down and refilled without problems.
My concern is that when the house was built the airing cupboard was immediately below the makeup tanks ( domestic and CH) with the extension the airing cupboard was moved to the other end of the hallway, thus all pipework (Supply and vents etc) now has to run the length of the hallway I don`t know if this is what has had an effect the the head !!!!

My temporary hose, which I connected yesterday, which raised the return by 1 metre has so far resulted in a cold makeup tank.
I have asked if I need a bigger pump as the radiators have doubled, but was told no ( a bigger pump; if available, may have made the problem worse anyway)

I am assuming due to the radiator circuit being changed and added to so dramatically that with the pump on full speed the `head` is lower than previously resulting in the spurting of hot water into the makeup tank.

Thanks

Calibra

 

[Agile]

A standard pump will run 15-20 rads or more.

The more rads then the lower the applied head so the less the likelyhood of pumping over.

Without seeing the layout of the pipework I cannot comment on the suitability.

Tony

 

[JohnD]

what makes you say you do not have a blockage? It could be a partial one causing a restriction in flow.

black sediment is very common on systems which are old and/or vented and/or were not consistently filled using corrosion inhibitor since they were built.

did you use a sediment-removing chemical?

 

[calibra]

Yes I used a flushing agent and then after flushing this out replaced it with a corrosion inhibitor, my circulating water is very clear.

Thanks

 

[sambotc]

A picture of the current pipework arrangement in the new airing cupboard would help

Sam

 

[Agile]

Yes I used a flushing agent and then after flushing this out replaced it with a corrosion inhibitor, my circulating water is very clear.

Thanks

What "flushing agent" was that?

Exactly what did you do with it?

Tony

 

[calibra]

Can`t remember it was a standard CH flushing medium.

Incidently the hot water is still returning to the makeup tank but at a much lower amount, it is just warm. This is with the return line elevated the extra 1 metre.