Hot water recirc pump sucking in air in the DHW tank?

Hi All

This is now problem 365 with our heating system. We have air in our hot water tank and it's most noticable when the HW recirc pump is running.

During this time you can hear the gurling and slushing and if you shake the tank, you can hear it slosh.

The HW recirc pump is on a CH controller and I've set it to come on for half an hour and off for half an hour to save wasted heat.

As I mentioned when the pump is on, you can hear the gurgling and when it's just turned off, I'm sure I can hear a hissing sound coming from the immersion heater.

I'm guessing that the seal for the heater is poor and the HW recirc pump is sucking air in there.

I'd like to take a look at it, but have never removed one of these before - so I guess I turn the cold feed off, half drain the tank and then remove the heater?

How is it attached to the tank? Screw in?
When it's out, how could I seal it? High temperature silicon runner?

If anyone can point me in the right direction, I'd be grateful.

Thanks

Steve

ps I've already done the flush trick by connecting the washing machine cold/hot together and this fixes it but not for long...

Can you take some pics?
Is there a normal vent?

Hi

It's a normal open vented system, with the vent going into the cold water feed. I've been searching the net since my post and found you can buy replacement immersion heater washers so I'll get one tomorrow, drain the tank down and see if fitting a new one helps.

I guess I'll need a big immersion heater spanner!

Wish me luck......

Steve