Glow-worm Compact 100e lock out problem

Robsop · 20 Feb 2008

I would be grateful if anyone could help me with this -

As a bit of background, the boiler has generally been working ok, although if anything the HW temp is lower that it used to be although some folk might put that down to external conditions.

The last few weeks I have experienced random boiler lock outs on the 100e model. Not frequent but say once or twice a week. The boiler is in the loft unfortunately so it is impossible to tell exactly when the lock out occurs and if it associated with HW or heating etc.
However, what I found yesterdays was that at times (not always) when their is a central heating demand the boiler is 'stopping and starting' every couple of minutes automatically. This can go on for indefinately and rads are still hot but if you click off using the thermostat, the demand light goes off but the boiler sounds like something is going on inside and then a few seconds later it locks out. Initial restart is not then possible unless the boiler is switched on when a hot tap is running - if you then close the hot tap the boiler then kicks in to central heating mode.

Any suggestions gratefully appreciated.

Whiter · 20 Feb 2008

It could be overheating? But if you click off using the thermostat do you mean the stat on the boiler? If so then the pump should be over-running to cool the boiler. When you run the hot tap does this cool the boiler, so that it can be reset?

Robsop · 20 Feb 2008

Whiter said:
It could be overheating? But if you click off using the thermostat do you mean the stat on the boiler? If so then the pump should be over-running to cool the boiler. When you run the hot tap does this cool the boiler, so that it can be reset?

Firstly, thanks for the help.

No, the stat I mean is the room stat.

Yes, I reckon that running the hot tap must do that. It wont reset if I dont do that first.

My theory is the thermistor on the CH is the problem. ie if this gives a false reading (low temp) then I assume gas would modulates higher than it needs to be (not sure why it switches in and out though). When room thermostat clicks boiler off - high temp in boiler causes lock out. Could replacing thermistor be the answer to the problem.

Also, could you confirm if thermistor actually modulates gas in accordance with temp setting on boiler or just switch gas on and off. Bit confused about how this actually works.

Thanks

Robsop · 21 Feb 2008

Whiter · 21 Feb 2008

If you can check with the manual and check the wiring of the room stat to the boiler. I think you still need to check that the pump runs after the room stat has been turned down thus cooling the boiler.

Robsop · 22 Feb 2008

Ok, my theory about what is going on here is as follows -

Up to about a month ago, boiler was ok but lock out problems occurred after I had it serviced.
Because the heat exchangers were cleaned out, I assume that even though the temp setting on the front of the boiler was kept the same, the actual water temp became higher because of the improved heat transfer. The CH setting has always been set to maximum.
With the boiler water running at this higher temp I reckon the temperature probe is either faulty of out of range as the signal is causing the boiler to stop and start every minute or so.
Once this stage is reached and the boiler stops via the room thermosat, the pump runs on to try and cool however the temp of water is such that the boiler overheat cut out operates the lock out circuit. (I assume because the hot water is pumped locally around the boiler circuit only and not the rads also.)

When the system had completely cooled down, I then set the CH temp (on the fronf of boiler) to about 30%. The flame is now set at a lower level which counteracts the efficiency increase in the HX and hence I assume reducing the CH water temp.
So far so good, rads are hot enough and boiler no longer cycles on and off with the subsequent locking out.

If I am correct with this assesment then I suppose its a bit of a fudge - the correct fix I assume would be recallibration of burner pressure and/or changing temp sensor on CH.

Can anyone confirm that I am correct with this.

Thanks.

Agile · 22 Feb 2008

Robsop said:
Up to about a month ago, boiler was ok but lock out problems occurred after I had it serviced.
Thanks.

Why dont you call back the engineer who serviced ( and apparently did other things ) ?

There seems to be other issues you have not mentioned if he was cleaning out water ways!

I dont like giving help to people who want to make up their own minds as to the problem because it always makes me think that they regard those who repair boilers as "not very clever". Whilst many are not the better ones are! Do you expect someone repairing your boiler to be a graduate?

Tony

Robsop · 22 Feb 2008

In that case then mate, dont bother helping.

If you look through my posts I have been polite in asking for some advice or assistance to help diagnose the issue.

I have spoken to my plumber (who I have a good relationship with) several time about this but we have been scratching our heads as to the root cause of the problem - hence posting on this forum and tapping into the knowlege and experience of the people on here.

I dont know why you have an issue with someone trying help diagnose a problem, sound like insecurity to me.

Its my policy to challenge (in the correct way) what any tradesman says, irrespective of his/her qualifications. Otherwise you might as well just get all the components replaced uneccessarily with the corresponding large bill.

Maybe you just cant bring yoursef to agree with diagnosis of a layman !!

Robsop · 23 Feb 2008

Quote from Agile in another thread - "I did a power flush for a BG customer (£350) which was totally unecessary!"

I rest my case.

[/quote]

Agile · 23 Feb 2008

Robsop said:
Its my policy to challenge (in the correct way) what any tradesman says, irrespective of his/her qualifications. Otherwise you might as well just get all the components replaced uneccessarily with the corresponding large bill.

There you go again! You have this expectation that any "tradesman", as you like to call us, will have no diagnostic skills and just change parts at your cost !

Clearly your "plumber" has few skills on boiler repairs but please dont judge us by his failings. You would be better engaging a boiler engineer instead of a plumber!

Whilst unfortunately there are many who do just change parts, most of the experts who answer questions free of charge on here are highly skilled at diagnosing boiler faults and are not just parts changers with a lower mental capacity as you suggest.

I dont like to be called a tradesman either! Its implies that you consider us working class!

Tony

Eeejit · 23 Feb 2008

.coming as i do from a long line of Eeejits
i bet my mental capacity is lower than....
what was i talking about???
where am i?

Whiter · 23 Feb 2008

Check your flow and return valves on boiler are fully open, and then check your rads for a by-pass route. Check that the thermistors are in the correct postion on the flow pipe.

Rob · 23 Feb 2008

The lockout light on could mean many faults.

The OH stat is wired in series with the primary flow switch. Lots of parts here could be a bit tempramental including the pump.

Id imagine the APS not activating would also cause lockout light.

Seen a couple of these gas valves sticking before aswell so again....

Start by having a visual check of the pump flow switch/microswitch for any leaks. Might be worth changing.

Oh stat not uncommon for these to cause trouble worth changing.

If you can confirm APS causes lockout again this might be worth changing.

sytec · 28 Jul 2011

I decided to answer this thread just for peoples information, i know that it is an old one.

it is not uncommon for an unscrupulous engineer to turn up the gas flow for the burner which in turn overheats the heat exchanger and causes the boiler to lockout.

this happens for one of two reasons
1. this saves the engineer the hassle of replacing a slightly clogged heat exchanger, if the call out was for hot water temperature.

2. ensures future call outs due to repeated boiler lockouts, which means he can say that you need a new boiler or some expensive repairs.

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Glow-worm Compact 100e lock out problem

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