Alpha CD28C hot water problem

[Stevemo]

I’m having trouble with the hot water from my Alpha combi boiler. The heating side seems to be working fine but the hot water starts off hot but then alternates between lukewarm and warm.
This problem only started when I replaced the pressure relief valve as it had been leaking and I was losing pressure.
When I first started it up after replacing the PRV the warning for low flow rate/pump fault came up.
My thoughts are that air has got into the system when I changed the PRV and become trapped?
Any advice on how to rectify this would be greatly appreciated.
Thanks

 

[ianmcd]

is the automatic air vent cap open ?

 

[Stevemo]

It was closed but when I opened it there was some air came out. If I leave it open there’s a small trickle of water coming out (I think that it needs replaced as well)
I’ve opened it up every couple of days and there does seem to be a small amount of air coming out each time.
If I continue doing this do you think it’ll eventually clear itself or is there a quicker method?

 

[martygturner]

Some rubbish in the heat exchanger...

 

[ianmcd]

yes they all leak so once bled i always close them, did you bleed the pump venting screw too

 

[Stevemo]

Pump venting screw?

 

[ianmcd]

Pump venting screw?

the large brass screw at the front of the pump, just crack it till air stops coming out, you may have a different pump depending on the age of the boiler, later ones had the ERP pump

 

[Stevemo]

Ah that looks familiar. I’ll give that a go as well as the automatic bleed valve. Hopefully the air will work it’s way through.
Cheers

 

[snb]

dhw plate heat exchanger partially blocked

 

[Stevemo]

the large brass screw at the front of the pump, just crack it till air stops coming out, you may have a different pump depending on the age of the boiler, later ones had the ERP pump

View attachment 265148

I’ve given that a go as well, still only tepid hot water
I put my ear up to the pump and it’s making a gargling noise like there is air bubbling around inside but nothing is coming out of the bleed hole ‍
Might have to bite the bullet and get someone out to have a look at it

 

[Stevemo]

dhw plate heat exchanger partially blocked

Sounds like an expensive job?

 

[Stevemo]

UPDATE -

The last of the air seems to have worked it’s way through to the automatic air vent valve.
Hot water now working as it should be.
Thanks for your help