Grant Vortex 15/21 non condensing - overheat stat?

[Bunker]

I went to this external Grant yesterday as it wasn't firing up. It wasn't locked out but controls seemed to be functioning - prog moved the control valve and got power to the boiler but no firing. The overheat stat nipple was extended as shown below and wouldnt reset (that is out isnt it?). The control panel of the boiler was slightly buzzing too which stopped when I pushed against the cabinet?! Anyhoo - I took the lid and control panel screws off and it suddenly started to fire up, seemingly all on its own. On arrival the boiler was completely cold, having been off for 24 hours so it wasn't the boiler stat settling and on arrival I threw the test switch but still didn't fire up.

Thing is, if the overheat stat is u/s - Id expect it not to run atall unless I bypassed it, I wouldn't expect the boiler to fire up with it stuck out.

Any ideas chaps?

Thanks.

 

[Roger Welton]

I'd probably put my money on the on/off switch had a few of them play up.

 

[Bunker]

Thanks for that Roger, does the oh stat look 'out' to you? it would go back in but not stay in.

 

[Roger Welton]

Nope, looks normal, when they trip there is more 'resistance' to them when you push them.

 

[kimbo]

I agree with roger

 

[kimbo]

A grant vortex 15/21 is a condensing boiler, it is basically a multipass with a secondary heat exchanger. It was called a vortex because of the turbulators in the secondary heat exchanger.

 

[Bunker]

Just had a call that's its gone out again. Thinking it through, I wonder if its the boiler stat going off but not auto re-setting....that sounds plausible eh? Ill get the meter on it.

 

[kimbo]

The boiler stats on these do not auto reset

 

[Bunker]

What makes the boiler run again after its gone out on the stat then?

 

[kimbo]

Presume we are talking about the overheating stat or have I missed something