Noisey Glow Worm Fuelsaver 80F

[Smartypantstoo]

Hi, I have a problem with an old Glow Worm Fuelsaver 80F - circa 1988.
Whenever the timer switches the system off or the room stat reaches temperature there is a load banging noise followed by a discharge into the header tank via the expansion system. However the noise does not occur when the boiler shuts off when it gets up to to temperature.
I have noticed that when the problem ocurs the pump is not running which I thought might be the heat overrun circuit so I replaced the thermostat control unit which also incorporates the pump over run circuit on this model of boiler. I have also replaced the overheat thermostat although I am pretty sure this would not be the problem. As a last resort I replaced the main controller board but this did not improve things either. All the radiators get hot and I have put some Sludge remover in the system. I have now run out of ideas, does anyone have any suggestions please? Many thanks.[/b]

 

[twgas]

Is the pump wired back to the boiler?

 

[Andygasman2010]

Is the pump wired back to the boiler?

If the pump still isn't running after demand with changing all those parts, it's probably not actually wired back to the boiler

 

[Smartypantstoo]

Hi, the pump is wired back to the boiler. Heating and hot water work fine except for the banging noise when either the roomstat reaches temp or the timer swithes the whole system off. Thanks.

 

[Andygasman2010]

given the parts you've changed and that you're sure the pump is wired back to the boiler, there's nothing left! Check the combined stat/overrun is wired correctly....

 

[twgas]

Is there a by-pass, and is it open?

 

[Smartypantstoo]

Hi, the wiring on the stat/overun circuit appears to be as per the wiring diagram and all connections are good.

 

[Smartypantstoo]

The doesn't appear to be a by pass but there is an expansion unit. This is working as you can here water being discharged into the header tank when the problem occurs. Thanks.

 

[Andygasman2010]

What do you mean by expansion unit??

Just to clarify, the pump DEFINATLY stops as soon as demand from the clock/stat stops? If this is the case then it can only be the combined thermostat/pump overrun unit. Change it again or have an RGI check it out for you.

A bypass is irrelivant if the pump stops as you describe.

 

[Smartypantstoo]

Many thanks Andygasman2010

I had kind of come to this conclusion myself but couldn't quite believe two units could have exactly the same faulty, especially one being a new one. Just wanted to see if anyone had any other thoughts before I blew another 60 odd quid.
Thanks again everyone.

 

[Andygasman2010]

If the fault isn't intermittant, you can do some wiring checks to confirm 100% that the overrun stat is faulty. I've just checked a wirring diagram i have, should be the same as the one on the case of the boiler.

on the overrun stat itself terminals 3 and 6 should be yellow wires, this is the thermostat and has nothing to do with the pump overrun. terminal 9 should be a brown wire which is the permenant live, terminal 8 should be a red wire which is the switched live from the controls, and terminal 7 is the purple wire to the pump

the overrun stat is basically a 3 pin microswitch opperated thermally. When it's cold there should be continuity between terminals 7 (pump) and 8 (switched live) and when it's hot there should be continuity between terminals 7 (pump) and 9 (permenant live) Do these checks with all three wires disconnected

Sounds like yours is stuck in the 7 - 8 position.

Phew! Lets hope that draws a line under that one ha, good luck