Boiler keeps going out

[paulmedd]

Gloworm 65/80 very old 25 years plus.
2 years ago boiler kept going out but not cured by changing thermocouple. Gas fitter said gas valve needed replacing and did so at considerable expense. Worked for a couple of days then same problem returned. I eventually found that the pilot light jet was partially blocked. Once cleared has worked fo 2 years.

So new gas valve 2 years ago. Problem now is that pilot light will stay alight when boiler is not running but goes out after about 5 min when running. Changed thermocouple to no effect. Gas fitter says gas valve gone again although even he found that difficult to believe. Said boiler was obsolete but was able to get used gas valve which he fitted when i wasn't there and reported that it behaved in the same way. He then lost interest and was put out when i wanted my new valve refitted.

Boiler makes lots of rumbling noises when heating, (is this called kettling?) which i believe is due to scaling or can there be other causes?My theory is that the vibrations from this rumbling is overcoming the weak hold on effect of the thermocouple. As i said pilot light stays alight when burners not alight and thus no rumbling.

Interested in your views please and how you go about adding descaler to system and what brand to use. System has not been serviced for at least 23 years possibly drained twice in that time.

 

[jdey]

Thanks for making me feel better. The burner unit on my boiler's only 11 years old, but I've been quoted for a whole new central heating system. I figured not many people would be willing to fork out that kind of money. Still at 25 years old it's 15 years past it's manufacturer serviceability date, and it's going to be much more cost effective to replace the boiler.

I know it's not your thermocouple, if that's any help. The thermocouple doesn't have any effect on how much gas enters the pilot light jet, it's used to control the gas valve which feeds the main burner unit. I'd get a decent plumber around but it sounds like the pilot light jet is partially blocked again.

 

[Agile]

Your gas engineer sounds pretty incompetent to me!

I would wonder if you have paid him as he has not fixed anything and has just fitted a new gas valve which was not required.

The gas valves are probably still available but thats not the problem as we know.

Perhaps you should get a competent engineer to fix it and get the first one to refund anything you have paid him.

Tony

 

[croydoncorgi]

Seems to me more likely that the 'rumbling' is because it's overheating and after 5 minutes or so the overheat limit 'stat is operating.

I'm struggling to identify this boiler.... is it a back-boiler? floor-standing?

 

[ChrisR]

Isn't it the one with a case about the size of a washing machine, pump on the right and a gas valve with a flattish hat shaped round knob (blue or white)?
Is the glass window still in place - it's important.

This sort of boiler attracts much praise of the "never let me down in 30 years" vein, until they spring a leak and do precisely that! Wouldn't dream of putting descaler anywhere near it, for fear of leaks.

I doubt they have overheat stats - ?
Would expect it to rumble and kettle, esp if the pump's worn out!

 

[paulmedd]

Hi,

Seems to me more likely that the 'rumbling' is because it's overheating and after 5 minutes or so the overheat limit 'stat is operating.

I'm struggling to identify this boiler.... is it a back-boiler? floor-standing?

Sorry should have mentioned boiler is very simple with thermocouple, overheat thermostat and 24v supply to main valve. When pilot light goes out there is still 24v on main valve and the overheat thermostat has definitely not tripped

Yes other people have trouble identifying the boiler although a net search shows it appearing just as Glowworm 65/80 in for sale details. Glowworm 65/80 is the only name on the boiler I have found. It is floor standing and I suspect it was installed in the 60/70's. It has a convection hot water circuit and pumped CH feeding two circuits one on same level one down. System has worked fine for 20 years but lacks any maintainance.

When I hold the gas feed pipe to the burners, you can feel the vibration from the rumbling. By hanging onto it and therefore dampening the vibration the boiler stays alight longer hence my theory.

Something else I should have mentioned is when I first started looking at the problem I diagnosed a shortage of water from all the gurgling and air in the system. Then I found the rads wouldn't bleed so suspected feed blocked. Visit to tank in loft found feed pipe at bottom corner of galvanized tank and whole corner over feed covered with sludge etc. Cleared this and run a curtain flex as far down the pipe as possible. Rads would now bleed and everything was fine for several weeks then the problems started as above.

My conclusion that the system is just clogged up with sludge and muck and it will do no harm to thoroughly flush out as this hasn't been done in over 20 years. That either the scaling or low water flow is causing localised boiling which is causing the rumbling and cracking which is causing the vibration which is shaking free the pilot light solenoid. The power produced by thermocouples is very low.

I need to do some uncovering work as I cannot see where the vent and feed join the system but am aware of good practice. I can see that pump is feeding straight into boiler rather than into system, however vent and feed do not join between pump and boiler.

I am convinced that there is nothing wrong with gas valve, thermocouple and overheat thermostat as all seem to be working perfectly. Clearly thermocouple and pilot light valve is working as this stays alight indefinitely when main burner not on.

Plan to remove pump and mains flush both directions and remove rads for flush and replace rad valves with special attention to feed pipe as I feel this may still be partially blocked. Ensure feed/vent in correct position and pump pumping in correct direction. Although as I have said system has run like this ok for over 20 years. Possibly also replace header tank with outlet not in corner or so close to bottom.

Thanks for help so far.

Paul

 

[ChrisR]

shaking free the pilot light solenoid.

I don't buy it. They make a surprisingly strong magnet, though a bad connection is always possible of course.

 

[paulmedd]

Isn't it the one with a case about the size of a washing machine, pump on the right and a gas valve with a flattish hat shaped round knob (blue or white)?
Is the glass window still in place - it's important.

This sort of boiler attracts much praise of the "never let me down in 30 years" vein, until they spring a leak and do precisely that! Wouldn't dream of putting descaler anywhere near it, for fear of leaks.

I doubt they have overheat stats - ?
Would expect it to rumble and kettle, esp if the pump's worn out!

Hi, Yes case size u state, pump on right, and there is a window to view the pilot light. There is an overheat stat. Gas valve is long rectangle box shape with blue knob as u say. 24v supply to valve with pilot light fitting on top of valve between main valve and knob. Gas in one end out other. pilot feed next to and on same face as gas out.

Yes I was worried about useing chemicals as boiler so old but I do like its simplicity and I very much doubt that modern boilers will still be going in 30 years. I would be happy spending a bit of time and money keeping it going as long as, as you say, it doesnt spring a leak!!!!

Yes could try changing the pump, its about due, has been replaced twice in 20 years. Hoever, when working can hear water circulating throughout house and all rads start heating. As the hot water circuit is convection should boiler not function ok without pump running anyway?

thanks Paul

 

[paulmedd]

shaking free the pilot light solenoid.

I don't buy it. They make a surprisingly strong magnet, though a bad connection is always possible of course.

Have cleaned mating faces up and ensured there is no "bits" leaking away current.

 

[Nestor_Kelebay]

Paul:

As you are already aware, if the thermocouple is in good condition, and it's sitting right inside the pilot light, then it should produce sufficient voltage to hold the "safety" electromagnet open so that gas will flow to the pilot light, and so that pilot light should not go out.

But, if it is going out, then something is happening that shouldn't, and you have to start looking at all of the things that might be putting that pilot light out that aren't normally a factor for consideration. Probably the very best way to find out exactly what is putting the pilot light out is to go down there and watch it through a boiler heating cycle and see if there is a strong draft or something that can explain it going out.

One thing that does fit all of your observations has been known to happened here in the Great White North, and that is the pilot light going out because the thermocouple cools down instantaneously when condensation drips onto it. (strange, but true)

What happens is that the chimney can cool down quite a bit when the boiler is not operating. When my boiler or hot water heater fires up, it's not at all uncommon to see water dripping down shortly afterwards. Flue gas contains water vapour, and if that water vapour in the hot flue gas comes into contact with a cold chimney or vent duct, that water vapour can condense into water droplets on the inside of the chimney or vent duct. And, if that water happens to drip onto the thermocouple after the main burners are out, it can cool down the thermocouple enough that the voltage it produces isn't enough to keep the safety valve open, and the safety valve closes shutting off gas to the pilot light.

Another thing that might be a factor is your clothes dryer. What MIGHT be happening is that when you turn your clothes dryer on, the blower in it is blowing air out of the house with gusto. If it turns out that the only place make-up air can get into your house is through the chimney, you can have a powerful draft of make-up air coming into your house through your boiler or water heater. And, the resulting down draft of air might be enough to blow out the pilot light. That may sound quite unlikely, but no one in here will say it's not worth investigating. Maybe try running your clothes dryer with both your kitchen and bathroom ceiling fans on, and see if your boiler's pilot light waves and flutters in the wind like the Star Spangled Banner flying proudly over Iwojima. If so, see if opening a window when the dryer is on corrects the problem.

Those are about the only things I can think of that would explain what you're observing. Sorry I couldna been more help. The real solution is to hunker down and watch your boiler's pilot light intently as the boiler operates. That's how most mysteries are finally explained.

 

[ChrisR]

I am assuming it's a room sealed boiler, so no chimney or clothes drier impact, but NK is probably right in his penultimate sentence. Pilot stability under operating conditions is important.
Your boiler probably needs a thorough service by someone used to the things, who would know what the pilot should look like. Pilot injectors do "wear out" for various reasons too. Yours may be obsolete. Anyone who doesn't know what they're doing could damage it.
Old gw's on gravity circuits, usually kettle quite loudly, especially at higher boiler temperatures.
If the HW primaries come straight off the boiler with vent and feed to those, leave the pump where it is - not much point moving it now.

Don't expect it to last long - start saving!

 

[dal5band]

Just an idea folks - could it be related to gas pressure. The main burner depriving the pilot circuit of gas?

 

[Nestor_Kelebay]

That wouldn't be plausible in my view. The 1/2 inch gas line going to the gas valve can deliver enough gas to fire the main burners and the pilot light simultaneously.

 

[Soggy_weetabix]

has anyone thought latent heat could be a factor. A sludged heat ex will trip the overheat without a pump over run.

David