Lock out/No pressure at gas control valve

[Daljit]

Hi

I've been having problems with my boiler for about 4 months now, where it would lock-out if demand switched on and off in quick succession, whether it came from DHW or CH. It would also lock-out if left running on CH after about 60 - 90 minutes. Ijust re-set it each time it happened.

So yesterday i had a go at repairing the fault - following the flowchart diagram in the manual, i decided to replace the sense electrode. I removed the front panel of the main burner in doing so, and as far i can tell i reassembled everything correctly. I also for some strange reason loosened the single screw holding the ignition box in place, removed it slightly, and then tightened it back up.

Anyway the result of this is that the boiler now fails to ignite at all. The fan and pump seem to be working, then after about 10 secs there's no ignition and the boiler locks out. (i even replaced the old sense electrode, but it made no difference)

I then tested the main gas pressure point, follwoing the manual, and discovered there's no gas pressure when a hot water tap is run.

Any suggestions on where i go from here? I read on this group that it may having something to do with a pilot feed being blocked or a blown fuse in the controller - is this something i should check? It's a Vokera Maxin combi.

Any advice appreciated.

ta

DAljit

[BigWallop]

Just a thought, but the sensor over the pilot flame may be faulty. Try holding a lighter or lit match under it for a few seconds, then try demanding HW and see what happens. If this doesn't work, then the pilot flame sensor and / or the detector at the main gas valve should be checked out.

[geoff]

In message , BigWallop writes

bugger all use I would think

its electronic ignition not a thermocouple - you need to provide a flame which is "touching" both the jet body and the electrode so that a current can conduct through it

OP - do you have 240 volts across the pilot solenoid ?

That should be the first thing to look for

[BigWallop]

So the spark lights the mains burner? Sorry, I've never seen a boiler that does that. I've seen the spark light a pilot flame, which in turn lights the main burner after the sensor and main gas valve detects that the pilot is properly lit and working.

[geoff]

In message , BigWallop writes

I read the post as there not being any gas pressure at the pilot - in which case simulating with a flame (what I fort you meant) wouldn't work

As an aside, I also think it might be a bit dangerous for someone who doesn't expect it to light the pilot (i.e. have the case open) with the potential for the main burner to come on and go WOOF

There are quite a number of boilers which have no pilot and light the main burner directly - the infamous Suprima, for example

[Chas]

so yoiu know f*ck all about electrics orboilers flame rectification so why dont you f*ck off off and lern about these things before you open your mouth on these things? you know f*ck all

[Ed Sirett]

[e-mail]...

Looks like this fault may have been introduced when looking for the original. The good news is that hard faults are fixable whereas "locks out after 90 mins" faults are almost impossible to find.

I'm not familiar with is model nor have I any manuals for it. I'm guessing its probably a fairly typical fan-flued, non-condensing combi. Very likely it uses one stage ignition lighting on the burner directly and flame sensing at the other end of the burner.

As with all boiler faults understanding the principles and following the sequence of operation is far far better than following fault finding boxes.

[geoff]

In message , BigWallop writes

I think that you have to be a little bit careful when it comes to boilers

If the OP had tried lighting the pilot with the cover off and it had gone up and removed his eyebrows (or worse) ...

[newshound]

I had problems a bit like this a year or two ago and I traced them to a filter at the inlet of the gas valve. This was partially blocked by flexible graphite debris, presumably from some type of seal upstream of the boiler.

[Daljit]

I'm not familiar with is model nor have I any manuals for it. I'm guessing its probably a fairly typical fan-flued, non-condensing combi. Very likely it uses one stage ignition lighting on the burner directly and flame sensing at the other end of the burner.

The above is an accurate decription of my boiler - there isn't a pilot, but there is a spark and sense electrode on opposite sides of the main burner - these are connected to the ignition box.

There's 20mbar pressure at the gas inlet testing point, but nothing at the main testing point which is less than 1 cm away!

I also notice when i switch the boiler on, i hear/see: fan and pump running, a click after about 4 secs, then nothing till lock-out at 8 -

10secs (presumably because there's no gas getting thru).

Problem seems to be with gas valve - perhaps debris. However, before i have a go at stripping this down (a big job!), could the problem be elsewhere? I appreciate not easy to say, but like i said, gas valve is a big job!

ta

Daljit

[Ed Sirett]

You have pretty much identified the problem as the gas valve. (did you disturb the connections perhaps when making other investigations).

It might be that the _ignition_ rate burner pressure is only 2 mbar. This may be quite hard to see on the gauge.

It would be helpful if you could see a voltage on the gas valve to confirm it as the problem.

Assuming it is the gas valve - these are one of the absolutely few genuine no user serviceable parts inside. Seriously don't even think of trying it on. A stuck-on gas valve will be just all too exciting.

[Daljit]

One week on... I actually went ahead and removed the gas valve, opened it (found nothing), closed it (making sure seals etc were tight) and reconnected - and boiler started working. I'm not sure if it was a mechanical fault or loose connection some place. From above, looks like i should now find myself a new gas valve.

The boiler is back to where i started - ie lock-outs when demand switches from CH to HW or vice versa.

I checked to the gas pressures and discovered HW should be 10mb but was around 17. Min and CH settings were out too, but not as much. This tweaking made no difference to the lock-outs occuring.

Re lock-outs - sometimes if the lock-out has just occurred, and you try reset the boiler, it doesn't respond - the boiler remains locked - the only way round this is to leave it for a few minutes (perhaps for some part to cool down). This type of local-out only v rarely occurs

- most times it resets immediately.

Further, i've noticed that the pump is very warm - almost too hot to touch. Is this normal?

Let me know if above gives you any more ideas about where the fault may lie.

Help much appreciated.

thanks

Daljit