Changed Rad, now heating okay but no hot water

Hi all,

Looking for help as my misses is about to hang draw and quarter me.

I moved a rad, and as a result drained some water off of the system using the drain cock on the downstairs rad. Rad moved all plumbed back in and system switched back on. Now however I have heating working properly, but no hot water and the DWH pump seems to come on when it feels like it, NOT when I turn the tap on.

I have also tried opening the drain valve under the hot water pump, it contains hot water. The drain tap above it on the way to the heat exchanger is bone dry however, I don't believe is is right.

I have removed/bled the DWH pump and a trickle of water comes out, it is also running continuously at a low speed.

The heat exchanger remains cold.

I have had intermittent issues with the PHE(T2) sensor showing -Err on the display.

I am at the stage where I think I have an airlock issue, and possibly a faulty PHE sensor.... Does anyone have any pointers?

Having called out a heating engineer, he spent several hours playing and changed sensors but couldn't get it working. Wanted to replace the thermal store sensor, but didn't have one so said he'd be back on Monday with a replacement one.

I was still convinced it was an airlock in the heat exchanger and that the thermal store possibly wasn't full.... It wasn't!

Using a feed to the drain, and venting off of the other valve above the dhw pump I fed water from the mains into the bottom of the tank until it started coming out of the other pipe, that took about a minute. My guess is that the airlock was preventing the pump from drawing the water around through the heat exchanger (it's designed to pump water not air), but also preventing the f&e cistern from filling the tank.

Symptom was: cold heat exchanger, everything else working.
Fix: manually fill thermal store, with bottom drain and allow air to escape via the valve above the DHW pump.

Next action is to drain some off again and add corrosion inhibitor, but also to check the cold water feed from the cistern is not blocked.

Have a good weekend all!