Pilot light keeps going out

[Nick]

I have had this problem for about a year now. The original post here:

a 12 year old Worcester combi boiler. When we use the hot water, it works ok for about 5 mins and then the pilot goes out hence the flames go out. We have to wait a couple of mins and then re-light the pilot after a few attempts. The hot water will then work for about 3 mins and then same happens again and so on. The central heating works fine and will carry on all night if necessary.

Originally we called out Britisg Gas (BG) as we have homecare. They had no idea what was wrong. I then complained and had 2 more visits. They could not fnd anything and just made up an execuse that my central heating was blocked up and needed a flush etc. otherwise they would not look at my boiler anymore. We had Transco check out gas pressure and they said everything was ok.

Come April/May and I was really fed of not being able to have proper running water so decided to replace the boiler. All of a sudden the problem went away. So we put the new boiler plan on the 'back-burner' and carried on with the old boiler through the summer months. Then towards end of Sept it started again and then got progressively worse. This weekend it went out and would not light up at all again. Note that this weekend is the coldest of the year so far.

I am no engineer but this points something to do with gas usage or pressure. First its nothing to do with CH blockage as CH works fine, its only hot water that triggers the pilot. Secondly the boiler worked fine during the summer months. Now that it is really cold it is worse. Could there be some issues with gas pressure?

I am going to cancel BG homecare because they have been useless. How do I get Transco to give me true facts? I am loathed to spend 2k on a new boiler installation just because there may be something wrong with the gas supply.

All ideas welcome.

[newshound]

When you run the DHW with the CH off, does the boiler seem to get noisier before it cuts out? This is the symptom with mine (no pilot light, and it cuts out sooner than 5 minutes), but it is cutting out on primary water over-temperature (hence sounds of incipient boiling) because not enough heat is getting transferred to the DHW through the partially blocked heat exchanger. Are you in a hard water area? In my experience, 12 years is a pretty good life for a modern combi.

Ed will probably be along in a minute!

[fictitiousemail]

Could the thermocouple need replacing .Cheaper than a boiler to see if it is that.

[Dave Liquorice]

I'd be tempted to replace the thermocouple and check the size and position of the pilot light flame. Though the fact that it works fine for CH is counter to a duff thermocouple or badly adjusted pilot flame. Does the CH use a different burner or different parts of the same burner compared to HW?

Note what another posted has said about more noise in HW mode just before it stops. It could be the overheat trip doing what it should due to the HW heat exchanger being scaled up.

[YAPH]

Good point. When you have to relight the boiler is there a reset button somewhere you have to press back in before it will relight? Does the thermocouple have either a couple of tags partway along its length, or where it's connected to the gas valve are there a couple of wires going off to an overheat trip switch?

If you can feel the flow pipe from the heat exchanger (inside the boiler, not the one coming out of the boiler to the CH - and take care you don't touch anything electrical while doing this) does it get much hotter on DHW than on CH? (An infra-red thermometer or some sort of thermometer you can get onto this pipe would tell you more accurately).

[Nick]

Yes it does get noisier with hot water but is very quite with CH. I had the gas pressure checked out and its spot on; no problems there.

So could it be just the blocked up CH system as BG claim? If so why didnt they address that in their annual maintenance programme or at least tell me about flushing.

[Dave Liquorice]

Unless they are being very loose with their terminology I'd say the CH system is fine and it's a scaled up heat exchanger for the HW.

Scaling of the heat exchanger is "wear and tear" TBH there is very little to actually routinely maintain in a room sealed boiler. They just work until a moving part wears out or scale builds up.

[Toby]

I am no expert, but if the CH works, and the DHW if the thing causing the boiler to trip out, I can't see the problem being with the CH side!

It could be a scaled up heat exchanger on the DHW side, resulting in the boiler calculating the flow rate and adjusting the burners to what it then thinks is correct for that situation, but then not getting enough heat away from the boiler, then the overheat trip triggers.

Do you live in a hard water area, if so, do you have anything to prevent scale, like an ion exchange water softener?

Toby...

[Nick]

They have been and this time figured out that some part had gone it. They returned next day with tha part (SW Stat??) - a little cumbell type device with 2 long leads. They installed this part and the pilot came back on and stayed on. They left.

However, the old problem still exists - when using hot water, it keeps going out every 4-5 mins and the pilot has to be re-lighted.

Also they said that the bolier is on a reduced parts list - they cant get all the parts for it. Its a Wrcester combi bought in 1996.