Boiler Overheats but BoilerStat working - update 4 yrs l8r!!

[jkennedyie]

Ehh, gravity fed oil fired central heating. New Riello Burner. Simple Boiler Stat (IMIT) with two thermocouples - regular (adjustable temp) and safety.

Stat doesn't shut down the burner when the water heats up, even when setting is min. Water gets terribly hot.

Assummed Stat was bust, so replaced, but same problem.

If I withdraw the Stat from the boiler and dunk the exposed thermocouples in a jug of warm water, it shuts the boiler down.

My current theory is corrosion/gunk inside the boiler around the thermocouple sleeve (which I haven't replaced) preventing the boilerstat from getting hot, but system only ~12 years old.

Anyone ever come across this before? Any recommendations for de-gunking?

Much obliged.

 

[Agile]

I think you need to review your use of the word "thermocouple" because oil boilers dont use them.

You have been doing a lot of DIY activity apparently without much idea of why you were doing it. You have not told us about the history either?

I am left doing some laterial thinking and I am left wondering for starters if your pump is operating in the wrong direction???

Tony

 

[ChrisR]

DOes the tube "thermal well" the thermostat sensor (which you're calling the thermocouple) is in, unscrew? You would get wet of course!

Boiler cleaning chemicals would probably help a bit, but I wouldn't expect a 100% fix.

You could try cleaning out the tube the sensor sits in, and thermally conductive compound (designed for the job) would help temperature transfer to the sensor.

 

[jkennedyie]

Sorry about my jargon. You're right, by thermocouples I meant the thermostat sensors (which seem to be based on thermocouple principle).

The stat sensors are indeed in a screwable tube / thermal well, but I am getting a professional in next week so probably won't unscrew it before then. Looks clean inside the tube. Thanks for the tip re thermal transfer compound...

The boiler pump hasn't been touched - direction there is fine also.

I have been doing more DIY than I intended. A little history...I got guys in when original burner died [was getting electricity + oil, but oil pump wasn't pumping] about a month ago, but they were chancers, so replaced entire burner myself (with model recommended by boiler manufacturers). That's when overheating seems to have begun. I since found a professional I can trust. He verified the stat wiring, but thought stat was dodgy (we observed sparking inside the stat), so I got a replacement, fitted it, but still no joy.

He'll be visiting me again next week to tune the burner, and I'll obviously get him to tackle this overheating too...

 

[Agile]

"""The boiler pump hasn't been touched - direction there is fine also."""

This forum is peppered with owners who say that things are fine when in many cases they are not.

I went to a 23 y.o. boiler this afternoon and the pump there has been backwards for 23 years!!!

You say that YOU replaced your oil burner yourself !

That would worry me and I would ask you how you set up the burner pressure and thus the input power?

Did you measure the temperature differential across the boiler flow and return?

Tony

 

[jkennedyie]

Greetings. Just wanted to update/close this thread in case others have similar problems...and get back to Tony. I did install the burner - it came preset for kerosene (my fuel). I knew it needed to be calibrated & always intended to get a professional out to do that.

Anyways, the professional came a few weeks ago
- replaced the boilerstat screwable tube / thermal well (alas there was no gunk on the original one when he removed it)
- verified wiring etc.
- fixed a tiny seep on one of the joints near the boiler
- calibrated burner (including emissions check)

No problems since.

So what was wrong? I now believe that I was wrong when I thought that the replacement stat was still allowing boiler to overheat. Turns out that the rads get hotter then I expected for the min stat setting (60), so I assummed it was failing. I think if I had waited a bit longer then the stat sensor would have heated up and shut down the boiler. Just with all the previous problems and dodgy stats I was a bit paranoid.

Thanks again for your pointers - have a good Summer.

- John.

 

[Agile]

After reviewing your original posting again, I have come to the conclusion that the probably main "fault" was that you had no heat transfer paste in the thermocouple pocket.

It was my omission to not notice that because you did not refer to it as if it was an important aspect and I tended to be more interested in the water flow because you have not measured the flow and return temperatures.

Coupled with that it could well be that the burner heat output was too high until the OFTEC set it correctly.

Motto, use a professional to check and set up your boiler and if you change parts take a professionals advice and NOT just the sales staff as they are NOT engineers or they would be earning double on the tools.

Tony

 

[jkennedyie]

I appreciate the valuable time that experienced folk put into this forum (and spent on this thread ~4 yrs ago). You might be interested in this update.

I thought this issue was closed, but 4 years later my system is still temperamental. Anytime professional plumber or I doing any work on the system over the years it has always been dodgy recommissoioning the system.

Last straw was last Wednesday week. I loosened and retightened a joint that had a slight drip. Since then hot water from oil boiler would not reach the house!! So I started to investigate over the coming days. I tried new NRV, new boiler pump (both correct direction). Still same problem.

Added drain valves on flow and return at the boiler and a stop cock on the flow and forced mains in various places to try and clear what I suspected was blockage or airlock under the house, but water flowed out the return fine. So no blockage between boiler and house on flow or return.

So the only other place for blockage was inside the boiler itself. Took off the pump. Forced mains in the boiler return, and nothing came out the boiler flow (at the pump fitting). Not a drop. Yep, pump valve was open and mains tap and hose were not frozen. Burner has been working fine and is at base of boiler so I believe could not be frozen internally. None of the pipes had frozen.

I couldn't believe it, and no plumbers I've spoken to can believe it either. It's a Grant 50/90. Phoned them up. Nice folks. No valves etc. internally. They have seen boilers clogging up eventually, but never one only 15 year/old.

I think a gunged up occassionally blocking boiler would explain all symptoms I've ever had with the system over the years.

It's an open system, and includes a back boiler. Water in f&e tank is a bit dirty, but not gungy, it is still consistency of water.

Had plumber over yesterday to see could he powerflush the boiler as my weak mains wasn't freeing it. He couldn't believe this would be necessary so investigated. He initially could drain water out of top of boiler, but then it stopped. Wouldn't refill through the return (in my opinion due to internal boiler blockage). But later either coz of some steam we created inside the boiler during the investigation, or running both boiler pumps at same time to see if weak pump an issue, I believe the blockage was freed up and the heating has been working perfectly since (on the one pump).

So unfortunately I wasn't able to prove the blockage to the plumber. He will look into other things more when weather better, and do some other jobs for me, but if anyone has come across similar blockage inside a boiler or can think of other explanation would be very grateful!!!

I will fit a second stopcock at the boiler to allow mains flushing of only the boiler without draining entire system when weather warms up a bit. Will refill the system with cleaner first.

I'm looking forward to seeing what comes out!!