occasional heavy knocking

[Biguns]

Thorn Appolo boiler system with cylinder and 3way valve. After Ch has been on for a while, occasionaly get heavy knocking when boiler fires up. Preliminary checks have found that this is caused by the pump not starting till the boiler has been firing for a while. Am I right in suspecting the 3 way valve?

 

[kevplumb]

pump should be wired through the boiler

if the boiler is firing ok but pumps not running

fault is prob in the boiler

which apollo is it

 

[Biguns]

pump should be wired through the boiler

if the boiler is firing ok but pumps not running

fault is prob in the boiler

which apollo is it

Thanks for your interest. Boiler is 20 year old Apollo 30/50B. The problem is intermittent but alarmingly loud, it usualy occurs after the heating has been on for an hour or so. the stat will demand heat, the boiler will fire but the pump will not, boiler will vent to expansion tank (hammering) then things will return to normal for a while

 

[kevplumb]

old un

there are 3 stats on it
1 high
1 low
1 pump overrun

you got a meter

 

[Biguns]

yes Ive got a multimeter

 

[kevplumb]

right try i assume you know how to use it

try belling the stats first

intermittent is a PITA BTW

dunno why but something is picking at me pump overrun stat

if you want the mi's put a e mail in your profile

or try partsarena

 

[Biguns]

PITA BTW ??

 

[kevplumb]

pain in the ass by the way

mi's sent

jeez a geordie

 

[Biguns]

Thanks a bunch for everything, sorry about the rule thing. Will commence fixing tomorrow. So its goodnight from my home town Washington (the original) UK
Good fortune Bill

 

[Biguns]

changing pump overrun stat has solved this problem. Thanks a bunch