Random lockout on Theocompact

[Toni's]

Can anyone help?
I was called to a vailliant thermo compact VU GB 282 E. The boiler intermittently fails on lockout. When re set it runs fine but then locks out again. I have changed the pump diff switch and small copper tube to the rear of the pump but still have problem.

Can an anyone advise.

 

[Anton]

Reckon your in the wrong forum, try gas safer register private forum.

 

[Dotty]

Not in the public arena.

Job 38.11

 

[Dotty]

Now Toni is in our gang, thread moved and reopened.

Answer away boys!

 

[Aquazone]

I'm not too hot on this model, but if there are minimum and maximum burner pressure make sure they are setup right.

If minimum is out when it modulates down may not be enoughh to rectify properly.

Also check resistance of thermistors and OH stat when it locks out.

 

[Rabbitman]

Hi Toni
is it the original thermo compact or the later /1 with the Honeywell gas, valve as the two need to be treated slightly differently in relation to the red lock out light

 

[Toni's]

Thanks mate.

 

[Leo21]

Can't remember that model axactly, I'd be looking a low burner pressure with the modulating wires removed or aps.

 

[Toni's]

its the later one, black facia panel, with three green dials and lights detailing fan,heating burner, and lock out, etc. the gas pressures have been checked, combustion is bang on in high and low flame. any ideas????

 

[Toni's]

its looks the same as the turbo max, but its a system boiler

 

[Leo21]

Is it first thing in the morning? If it is could be governer. Have you seen it lock out? Is it firing and then locking out, or on fire up?

 

[Toni's]

it can run fine for couple of hours, then on its next fire up, goes into lockout. don't try to spark, fan don't run, hence why i thought it was something to do with the pump dif switch, not detecting a flow.

 

[Toni's]

happens randomly throughout the day

 

[Leo21]

Clean the tubes out on it, can you see if the switch is making?

 

[Toni's]

What tubes? i have changed the little copper capillary tube at the back of the pump, that was found to be partially blocked.

 

[gasmanrob]

If there's a blockage it shouldn't appear randomly it's either there or it's not. Pull the pressure switch apart if you've already replaced the differential tubes 9/10 times there is crud on the underside which will effect its operation but like I say it's usually all or nothing.

personally I'd say check the transformer out had a few on this model that once warm won't operate. And also check that the air pressure switch returns to NC as if it hasn't the boiler will not go through its start cycle in this instance though the fan illumination light is usually on before anything has requested demand or operation

 

[Toni's]

Thanks, will pick up a transformer and APS, i have already replaced the pressure switch and tube. will give it a go tomorrow and let y'all know how i get on.

thanks for your help

 

[gasmanrob]

Easy on throwing parts at it though those are only possibilities don't forget. I wouldn't want anyone wasting money on something that is only a possibility

 

[gasmanrob]

If you do find the aps sticking clean the tubes and the Venturi if it's near a busy road with lots of hgv traffic the soot and stuff can often build up in these areas and prevent free flow of air. And carefull removing the Venturi they can be as brittle as a cracker soacked in vinegar

 

[dancinplumba]

Am ere 🙂

 

[mountainman]

You've cleaned the water flow sensor pipes but have you checked the venturi on the pump? I had a few if these block.

 

[Leo21]

Am ere 🙂

Cryptic as ever Dancin.

 

[gasmanrob]

Any update on this? Was a big song and dance would be nice to know an outcome

 

[Toni's]

Yes Sorry guys, did'nt mean to leave you all hanging, its just that i didn't want to tempt fait. Waiting for a call from client in the morning with an update. Mountainman was bang on. The venturi on the pump manifold was blocked with black crud, cleared with a fin piece of wire and blew through with some compressed air. Re-assembled all good so far. Will up date you in the morning.

 

[Toni's]

Thanks for everyones advice, the boiler seems to be working well, client happy thats the main thing. Cheers all.