johnws
There are a couple of unanswered questions. 1. Is this a problem that has just started? 2. How much hot water are you using ie. could you be using all the hot water in the cylinder before it has had a chance to recover?
When water is heated, it expands at a rate af about 3%, this would equate to about 1 gal for a 40 gal cylinder being heated from cold. .
I recommend you turn off the power to the cylinder turn on a hot faucet for approx 1-2 seconds and see if the valve starts to relieve again. If the water stops then it may only be operating as it should. If it doesn’t then follow the instructions of Harold and Lyebury and get a professional.
