unvented hot water cylinder problems

[sasik]

My customer have a Santon unvented hot water cylinder. The cylinder will discharge water when the system heats up (it will run water constantly from the discharge pipe).
I tested the pressure in the expansion vessel and in the hot water outlet when it was discharging and the pressure was over 6.5bar in both! I then drain the system down and the pressure in the vessel was very low so I recharge it back up to 3.5bar.
I refilled the system turn the boiler on and when the system heated up it discharged again!!
I tested the pressure again in the expansion vessel after I drined the system down and this time the pressure was 3.5bar fine! I tested the pressure in the hot water outlet point and the cold outlet point and the pressure is fine (equle pressure 3.5bar).
I know the high temp' relife valve is fine and I also know the combination valve/pressure relife valve is fine (it's brand new).
So what could be the problem

Thanks Sasi

 

[traineedrip]

My customer have a Santon unvented hot water cylinder. The cylinder will discharge water when the system heats up (it will run water constantly from the discharge pipe).
I tested the pressure in the expansion vessel and in the hot water outlet when it was discharging and the pressure was over 6.5bar in both! I then drain the system down and the pressure in the vessel was very low so I recharge it back up to 3.5bar.
I refilled the system turn the boiler on and when the system heated up it discharged again!!
I tested the pressure again in the expansion vessel after I drined the system down and this time the pressure was 3.5bar fine! I tested the pressure in the hot water outlet point and the cold outlet point and the pressure is fine (equle pressure 3.5bar).
I know the high temp' relife valve is fine and I also know the combination valve/pressure relife valve is fine (it's brand new).
So what could be the problem

Thanks Sasi

sludge in the expansion vessel connecting pipe or other blockage?

Have any extra rads been fitted?

 

[Plouasne]

My customer have a Santon unvented hot water cylinder. The cylinder will discharge water when the system heats up (it will run water constantly from the discharge pipe).
I tested the pressure in the expansion vessel and in the hot water outlet when it was discharging and the pressure was over 6.5bar in both! I then drain the system down and the pressure in the vessel was very low so I recharge it back up to 3.5bar.
I refilled the system turn the boiler on and when the system heated up it discharged again!!
I tested the pressure again in the expansion vessel after I drined the system down and this time the pressure was 3.5bar fine! I tested the pressure in the hot water outlet point and the cold outlet point and the pressure is fine (equle pressure 3.5bar).
I know the high temp' relife valve is fine and I also know the combination valve/pressure relife valve is fine (it's brand new).
So what could be the problem

Thanks Sasi

Is the diaphragm in the expansion vessel sound??, and how big is the vessel in relation to the cylinder?? with regard to the expansion of the water

 

[justlead1]

Hi Whats the relief valve working pressure?

 

[Plucky]

Although you say you think its ok I would change expansion/pressure relief valve.

 

[sasik]

sludge in the expansion vessel connecting pipe or other blockage?

Have any extra rads been fitted?

No extra rads on the system but maybe sludge in the vessel. I take it, a new vessel required.

The diaphragma is fine, no water coming out of the small air valve at the top of the vessel. The vessel is the original one that came with the cylinder so it will be the right size.
The pressure reliefvalve set at 3.5bar working pressure and it will discharge at 6.5bar.
I all ready replaced the combination valve (pressure relife/pressure reducer/strainer) but I might replace the expansion valve as well.