Boiler diagnostic help, please. This one's baffling me!

[Masood]

Custard has a Glow Worm 24ci, which is doing something odd.

Hot water fluctuates hot/cold which sounds like classic blocked PHEX. BUT - this is the baffling bit - when she has heating on, hot water runs fine, at a constant temp. Which, given that the diverter should cut off the CH side, is very odd!

I descaled the PHEX a couple of months ago and it wasn't that bad at all.

Any guidance, ideas or input gratefully received!

 

[kris]

Hi masood did u check the resistance on the dhw thermisor , and is there a flow switch outwith the diverter ( maybe not). I do know that the glowworms have a badly designed condendate trap on some of there models ( the top of the trap has a blue plastic insert with spade connectors linked to pcb and because its a bad design flaw and has been changed the boiler often thinks the trap is not draining. But this would hapen on heating circuit aswell. Check thermistor.Also does heating work perfect no fluctuations with that?

 

[kris]

Could be that your diverter is .sticking

 

[kris]

Is that model a condenser?

 

[dazsl]

more than likely to be the diverter sticking

 

[mountainman]

I had the same prob recently and it was the phex partially blocked on the heating side.

 

[Ermintrude]

Git says plate or returning spring on div freckles

 

[stevetheplumber]

does it leak down the heating when the hot water is on?

 

[Masood]

Hi masood did u check the resistance on the dhw thermisor , and is there a flow switch outwith the diverter ( maybe not). I do know that the glowworms have a badly designed condendate trap on some of there models ( the top of the trap has a blue plastic insert with spade connectors linked to pcb and because its a bad design flaw and has been changed the boiler often thinks the trap is not draining. But this would hapen on heating circuit aswell. Check thermistor.Also does heating work perfect no fluctuations with that?

Will check thermistor, not sure about fluctuations on CH side, as not been yet.

Is that model a condenser?

No Kris, non-condensing

does it leak down the heating when the hot water is on?

Haven't been yet, just what the custard said.

 

[Leo21]

If hw ok that proves primary hex and dhw hex ok to my way of thinking. Which leaves diverter not opening properly on ch.
Not familiar with that particular boiler tbh, just my logic.

 

[Millsy 82]

Check burner pressure. If it modulates look at thermistors if it cuts out completely then fires up again look at blockages pump running slow. If you have heat leaking into the heating circuit then look at diverter.