Problem with boiler - High Limit stat cutting out

rob w

Hi,

Having a problem with my boiler and not exactly sure what might be causing it. First noticed yesterday when it didnt heat the water/rads as expected.

It seems to be kicking in intermittently when heat is called for. Opened it up today to have a look.

• Photocell is clean, thought that might be it originally, but seems fine.
• No leaks in fuel line, loads of oil in tank.
• Pump is circulating fine, only replaced a few months back. Rads are heating when it is actually running
• The boiler is not locking out - as in the red light is not coming on when it stops, and dont have to do anything to restart it

However, it seems to be the high limit stat that's stopping the boiler - turning it up a fraction, I can hear the click of the stat and the boiler fires up

So what could be causing the problem here. Could be a faulty stat? But may be some other underlying issue Im not aware of. Im an electrician, so comfortable enough with the electrics, but not 100% up to speed on what could be causing issues like this in the boiler/burner itself. Would it be worth replacing the stat incase its faulty or is there something else to consider?

I've added a photo too - the stat I'm talking about is the one in top right corner. Boiler is a Firebird Silverpac 26 kW

Thanks in advance

1709200569939.jpg

rob w

Also, just thinking about it now. I have a infrared thermometer so I could measure temps to see if the stat is actually cutting out at the right temp or not.

Just not sure what location it should be measured at on the pipes?

John.G

Its not the Hi limit stat thats tripping the boiler, if it was, you would have had to remove the little plastic cover (near "Firebird) on the stat box and press the reset button, it operates at ~ 110C/113C, its the control stat thats switching off the burner and then refiring the boiler, it looks to be set around 65C ish, so its cutting out at 65C and refiring at ~ 55C, IMO you have a circulation problem. Possibly the control stat not resetting but turning it up and down should give you a fair idea if its OK there should probably be a division or so difference between cut in/out.

Even if the hi limit stat operated it doesnt bring up the lockout on the burner.

Can you post or photo all the pump data, make/model/mode/setting, if it is a A rated pump with LEDs, post a photo of the LED status, (pump running).

Wearb

Agree with John. Likely to be pump, or lack of water in the boiler/system.

rob w

Thanks for the reply - yeah you are right its the control stat rather than the high limit, wrong terminology used in my original post

Some photos attached there now.

When I call for heat, the pump runs and starts with 3 lights on it. Then it changed to no lights on. Boiler still running though and rads heating, for a while at least once I turn the control stat up a notch.

About 6 weeks ago I replaced a leaky blanking plug on a radiator. Followed the steps in this video - could that have anything to do with this issue? Maybe I trapped air somewhere?

https://www.youtube.com/watch?v=hj7SDfMQVWY

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John.G

The pump should stay running with the lights on as long as the boiler is firing, I would check for voltage still present in the pump/wiring terminal box when its stopped if boiler is still running. First check as suggested above that there is water in the system, if a open vented system, check for water in the small F&E cistern in the attic, if a sealed system, check pressure, should be 1.0bar/1.5bar.

zg3409

As said likely to be no water in system or air lock. Did you turn any valves anywhere recently and could they still be off?

rob w

I just bled A LOT of air from one of the big upstairs rads. No air in any of the others.

Probably there as a result of me changing the blanking plug a few weeks back.

Could that have caused it?

Pump still running when the boiler is firing. I'll check the F&E tank in the attic later when I get a chance.

John.G

As you look at the upside down pump while running see which mode is highlighted or has the arrow pointing at, keep the mode button pressed until the bottom curve is selected which is constant curve or fixed speed then if required just press the mode button briefly to get just one LED, this is a 4M pump head setting which should be adequate. If it was set to full 3 LEDs then 7M will definitely cause air in a open vented system, keep venting the air regularly. If this settling is not heating all the rads change to (constant curve) 2 LEDs. How many rads? if you have pump instruction book try and post a photo of the pump curve settings from it.

⁹

Wearb

Is your condensate pipe just terminating in the bottom of the boiler casing?

declan b

https://www.boards.ie/discussion/comment/121833251#Comment_121833251

Id say your correct going by the white power substance on the casing. its a poor boiler install

declan b

There is a very obvious issue with the boiler install. ive never come across it before. any of the service guys spot it...

jimf

that fire valve is really doing its job

declan b

spot on!!

rob w

No, it's connected to a black pipe that goes into a drain beside the boiler. It's just hard to see in the pic

But yeah, I agree, it's a bit of a messy looking job. We just moved into the house last year, had it serviced by a local guy... Not the original installer, and he never mentioned any issues to me.

What's the issue with the 'fire valve', you'll have to educate me?

rob w

And the boiler is back operating as normal since I bled the upstairs rad yesterday.

declan b

The firevalve is fitted in the wrong position, it should be fitted before the tigerloop.Ideally it should be a remote acting firevalve.

Ideally the tigerloop should be an internal tigerloop if fitted inside the boiler casing.

jimf

https://www.boards.ie/discussion/comment/121836943#Comment_121836943

jesus your very exact

in your old age

rob w

And what are the implications of having it installed the way it is?

What do I need to get a plumber to do to sort it?

Thanks

Lenar3556

https://www.boards.ie/discussion/comment/121838823#Comment_121838823

If there was a fire within the applicance the oil would continue flowing and feed the fire. The current fire valve should be removed and instead fit a remote acting fire valve on the incoming oil line to the tiger loop.

A small job, but an important one. The rest of it isn’t too bad. Keep it well serviced, that wouldn’t be the best boiler design in the world and if it soots up will be very difficult to clean.

Wearb

https://www.boards.ie/discussion/comment/121838823#Comment_121838823

Get a pipe put on the pressure relief valve. Have a stainless steel trap fitted.

Is your oil tank below the level of the burner?

rob w

https://www.boards.ie/discussion/comment/121839020#Comment_121839020

Oil tank outlet is just slightly above the level of the burner I would say

Is the installation of a pipe on the pressure relief valve and a stainless steel trap in addition to moving the fire valve, as per Lenar3556 post?

Whats the purpose of the pipe on the prv and the trap?

Wearb

The pipe is to prevent a leaking prv from flowing down on electric items.

Those old plastic traps have been known to melt.

rob w

Thanks for the help on this one so far!

Boiler had been working as normal since last week. However, has started acting up again this morning! 😩

Turned rads on this morn, and they only half heated up. Went out to the boiler and its kind of stuttering - its making a constant running noise, and it tries to kick in fully (trying to ignite I think?) but only does that for a second and then tries again a couple of seconds later. Its just stuttering its way through that loop constantly, so its kind of heating but not fully.

Whats could be causing this behaviour now? Ive a video attached there to hear the sounds its making (Ive had to save it in a powerpoint file as it wouldnt let me upload an .mp4 video ......and don't mind the pesky crows in the background!!)

Boiler.pptx

Lenar3556

Dirty/faulty photocell maybe, but several other possibilities.

You would be best to get a boiler guy out to sort it out, and resolve the other few bits while he is at it.

rob w

Thanks, yeah I think I have resolved myself to calling in a boiler guy now. Due an annual service anyway. Thanks

rob w

Jesus its hard to get people out to do work like this these days!

A few just turned down the job straight away, the guy I did get has quoted €180 for an annual service (OFTEC service) - is that a bit on the high side? Seems to be from the last time I remember getting a service (gas boiler in previous house)

Lenar3556

Depends on what is doing for that - probably a bit on the high side. You need more than a service though

New nozzle

new flexi hoses x 2

pipe down prv

replace plastic trap with stainless.

fit remote fire valve

Identify and fix current firing issue

clean boiler and set up combustion.

You are probably looking at €300-400

foxhunter2024

Interesting thread there, open to correction but should the pump be rotated to vertical or is it photo taken upside down?

I see the fire valve the old type, should that not be 1 metre from boiler?

jimf

https://www.boards.ie/discussion/comment/121877065#Comment_121877065

old type wheel head valves as near as possible

new type rafv ideally i metre but at least outside the boilercase

foxhunter2024

https://www.boards.ie/discussion/comment/121877103#Comment_121877103

That installation is technically correct even though it should be a remote one?