Boiler heating hot water cylinder only on hot water and heating demand

[Iain Hunter]

Boiler heating hot water cylinder only on hot water and heating demand

Hi all

i have a problem, at a job where the boiler only heats the hot water cylinder when the hot water and heating are on demand via programmer. When on just hot water the flow gets hot but the return doesn't, then the boiler over heats and locks out, on just heating all works fine. It's a 3 port valve that is fitted on the system which is working find. Any suggestions?​

 

[lame plumber]

flow to the valve gets hot or flow fm valve to cyl gets hot

 

[Iain Hunter]

Flow from valve to cylinder gets hot but not the return then the boiler over heats

 

[Whn1]

Is there a gate valve on the return?

 

[lame plumber]

sounds like the valve isnt opening properly so motor on way out, ie it cracks open enough to allow a weap by but not a proper flow

 

[Iain Hunter]

No gate valve on return

 

[Whn1]

Blocked coil?

 

[lame plumber]

motors knackered!

 

[Iain Hunter]

sounds like the valve isnt opening properly so motor on way out, ie it cracks open enough to allow a weap by but not a proper flow

Ok, this could be a possibility, but even with It slightly open why would the flow get hot and it not return to boiler? The pump is still running after boiler goes to overheat. It obviously is opening fine when on hot water and heating demand together

 

[Iain Hunter]

Blocked coil?

New cylinder also heats up fine when on hot water and heating demand together

 

[lame plumber]

because it does

 

[dancinplumba]

Are you THE Iain Hunter ?

 

[CM25]

Replace the whole 3 port, sounds like a problem with the valve section.

 

[Iain Hunter]

Are you THE Iain Hunter ?

The real deal, yep :yes: