Overflow problems with Range Tribune HE Direct

[Fran1948]

Hi - I hope someone can assist me.
I have a problem with a Range Tribune HE Direct 150L (Electric non-vented) cylinder that was fitted in my property in 2005.
When the heater is switched on I lose hot water through the overflow pipe, via the TPR15 control valve (this usually occurs between 30-60 mins of being switched on)
This problem only occurs when the heater is switched on.
A pumber has been out to fit 2 new thermostats but the problem still continues.
Has anyone got any suggestions as to what else we need to consider in stopping the overflow?

Thanks in advance,

Fran

 

[John506]

Did the plumber check the expansion vessel?

Or if cylinder is a bubble top, did he drain and re-fill to recharge the bubble?

 

[Fran1948]

Hi John,
Thanks for responding. Yes, the plumber did check the pressure in the expansion vessel and everything was in order.

 

[MJN]

If the stat and expansion vessel have both been checked then the only possible culprit is the TPR valve.

The only odd thing is why the plumber hasn't already ruled it out (is he qualified to work on unvented cylinders?).

Mathew