Worcester greenstar, Hot water intermittent.

[Ted808]

Heating works and hot water- sometimes, but I noticed when I turn the hot tap on the pressure gauge drops to zero.
I've not seen this before. Topping up the pressure doesn't seem to make a difference. As soon as the heating only is on pressure goes back up to 1.5bar.
The thing is the flat is disgustingly filthy and I don't want to spend ages there... So if anyone has any pointers- much appreciated.

I'm thinking dirty line to PG and PV flat. Now can you get a blockage between the PG and the HW path only?

 

[ShaunCorbs]

Check the diverter flap isn’t stuck
Check when hot water is running no flow is going down the htg flow

Other than the flow switch or plate it should work

Never need the guage go to zero on one tho then back to normal

 

[Ted808]

Check the diverter flap isn’t stuck
Check when hot water is running no flow is going down the htg flow

Other than the flow switch or plate it should work

Never need the guage go to zero on one tho then back to normal

Yeah I've never seen that either. Can't fathom it.

 

[Chuck]

I can't think of a single-component cause but, if I've understood the OP's observations correctly and the pressure changes are relatively rapid, a combination of faulty expansion vessel and a PRV that is passing at 1.5 bar might fit the bill.