CH Header Tank Overflow Problem

[timh]

I have a problem with the Central Heating header tank overflowing caused by water entering the tank from the expansion pipe that feeds into the tank. The Tank overflows when the boiler and pump cut in. My system is a conventional fully pumped with an electric Y valve to distribute hot water from the boiler between HW system and CH. Any suggestions as to what the problem might be?

 

[stevew451]

try turning the pump speed down if possible

 

[timh]

Many thanks I'll try turning the pump speed down and let you know if successful

Have tried turning the pump speed down from 3 (been on that setting for years with no problems) to 2 but no effect leak from CH header tank overflow pipe is just the same. Is it likely to be corrosion in the hot water cylinder heating coil? Although water is not entering the cold water header tank it's going into the CH header tank

 

[doitmyself]

I have a problem with the Central Heating header tank overflowing caused by water entering the tank from the expansion pipe that feeds into the tank.

Do you mean the pipe which hangs over the header tank like an upside down J?

If so, how far above the water level is the top of the loop?

How high is the water level in the tank when the system is cold?

If you drain some water from the system does the level in the tank go down and the ball valve open? (Lock the lever on the motorized valve in MAN position when you do this.)

 

[timh]

Many thanks for the reply.
Yes the pipe is the one that hangs over the tank like an upside down J
Work commitments mean that it will be Sat before I can get up into the loft again
From memory top of the loop is around 50cm above the water level
When system is cold water level in header tank is just below the overflow outlet
I will try draining some water from one one of the downstairs radiators on Sat and let you know what happens

 

[fuzzy]

I have a problem with the Central Heating header tank overflowing caused by water entering the tank from the expansion pipe that feeds into the tank. The Tank overflows when the boiler and pump cut in. My system is a conventional fully pumped with an electric Y valve to distribute hot water from the boiler between HW system and CH. Any suggestions as to what the problem might be?

The expansion pipe or the vent?

the vent should be 22mm and loop over the top of the tank. this shouldnt have water coming out at anytime reallly, all expansion should come up the cold feed

 

[doitmyself]

From memory top of the loop is around 50cm above the water level

That's OK

When system is cold water level in header tank is just below the overflow outlet

The water level when the system is cold is much too high. When the water in the system heats up it will expand, so the level in the tank and in the vent pipe will rise and go out of the overflow.

The float arm of the valve need to be bent down so the valve open just before the water level reaches the opening - say an inch above. This is to prevent air accidentally entering the system.

This then leaves enough space in the tank to accommodate the expansion of the water. This is about 4%, so a 100 litre system will expand by 4 litres. The typical tank holds about 18 litres.