Boiler Overheat

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Old 04-17-13, 08:08 AM
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Boiler Overheat

My Grant Euroflame boiler overheated, spewed water from the system expansion tank and the limit stat on the boiler kicked in. Its a fully pumped system with circuits for upstairs heating, downstairs heating and hot water.
I replaced the dual stat on the boiler but it still overheats.
Problem seems to be that boiler is heating when no demand for heat from CH or HW thermostats (is this normal?). As there is no pump running the boiler overheats (when I force a pump to run, the stat on the boiler works properly).
So: Should the boiler be firing with no demand from the system ?
If No then the controller is broke right?
If Yes then would something like an airlock or sludge cause the overheat?
 
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Old 04-17-13, 08:24 AM
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What tempurature is the boiler overheating at?
What is the pressure reading on the gauge?
 
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Old 04-17-13, 09:33 AM
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No pressure gauge in the system, its not sealed, so don't know the pressure.
Limit stat is factory set to ~110C.
 
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Old 04-17-13, 09:51 AM
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So you are saying there is not gauges on your boiler?
110'C is above boiling point (230'F for the American folks).

Did this overheating (very high temps) just start, or did you just happen to notice it due to the water?
 
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Old 04-17-13, 12:34 PM
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We only noticed because the limit stat kicked in and stopped the heating working.
But now that I piece it together there was occasional unexplained water near where the expansion tank overflow exits the house for some weeks now.
 
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Old 04-18-13, 05:15 AM
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Can you post some pictures of your setup?
An overall photo or two and then some closed ups.
The more photos the better.
 
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Old 04-18-13, 05:56 AM
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One thing to note here... I believe this system is located in the UK and most of us here are on the other side of the big water. Heating systems are significantly different there and we may not have experience with your particular brand.

I believe that your expansion vessel has failed. With a defective expansion vessel, when the water is heated there is no place for it to expand and it will open the pressure relief valve and you will have discharge.

This problem may only partially be related to the temperature.
 
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Old 04-18-13, 10:06 AM
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you should be able to determine quite readily whether or not the boiler is firing when there is no call for heat.

If it does, then disconnect the TT connection at the boiler.
If it still fires, then look into the boiler controls. If it does not then it's what every zone controls you may have or a bad stat.
It's hard to know with out knowing much about your system
 
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Old 04-19-13, 01:55 AM
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Hi Guys, thanks for all the responses.
Working on the pics, need to charge a camera.
Is there an expansion vessel on a non-sealed system?
Yes I am in Ireland (but water still boils at 100C here ;-)

The boiler IS absolutely firing with no call for heat, most of the wiring diagrams I have seen suggest this is NOT the way it should be. What is the TT connection?
Is there any scenario where a boiler should fire with no call for heat ?
In my system, the stats seems to only turn on the circulation pumps (there is a timer on the boiler, regardless of it being on or off, the room stat and hot water stat turn on circulation pumps)
I have put the manufacturers manual for the boiler at the link below.
I have the 50/90 boilerhouse model and my system is a fully pumped (non-sealed) setup with separate pumps for underfloor heating, hot water, & rad heating.
https://dl.dropboxusercontent.com/u/...ILER-HOUSE.pdf
 
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Old 04-19-13, 01:58 AM
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The quality of some of the diagrams in that manual is very poor.
I've put a manual for a very similar boiler here:
https://dl.dropboxusercontent.com/u/...tions-2003.pdf
The diagrams much clearer in this.
 
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Old 04-19-13, 05:00 AM
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will look at it in a few hours
 
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Old 04-19-13, 05:12 AM
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Sounds like the aquastat is configured the same as mine use to be.
My two zones (t-stats) where connected to relay boxes and to the circulation pumps. There was no direct connection from the relay boxes to the boiler or aquastat.
What this did was allow my boiler to maintain the water temp between 140-175'F, regardless of heat calls.
The benifit I can see with this is that the boiler doesn't fire so frequently if you have an older aquastat with a small diff range (and are under radiated as I am).
I'm now configured to have the boiler fire only on heat calls and shut down when the call is satisfied or the hi limit is reached. The good about this is it doesn't fire if it's not needed. The bad is that it fires more frequently during heat calls because it's got a non-adjustable diff of ~10'F.
 
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Old 04-19-13, 07:01 AM
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OK, so it IS a legitimate way to configure a system. Seems crazy to me that a call for heat can turn on a pump regardless of whether the boiler is firing or not.....unless it assumes the boiler will be hot.
So the problem must be in my boiler. For some reason the boiler stat doesn't properly measure the water temperature at the heat exchanger (unless there is a circulation pump running). It had been running properly for some 7 years now so whats changed ? Clogging ? Airlock ?
Guess I'm going to need a boiler guy. OR I could re-configure the system to make it that the boiler only fires when there is a pump running. Whats my best option?
 
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Old 04-19-13, 08:05 AM
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OK, so it IS a legitimate way to configure a system. Seems crazy to me that a call for heat can turn on a pump regardless of whether the boiler is firing or not.....unless it assumes the boiler will be hot.
So the problem must be in my boiler. For some reason the boiler stat doesn't properly measure the water temperature at the heat exchanger (unless there is a circulation pump running). It had been running properly for some 7 years now so whats changed ? Clogging ? Airlock ?
Guess I'm going to need a boiler guy. OR I could re-configure the system to make it that the boiler only fires when there is a pump running. Whats my best option?
I'm not sure what the thought was behind that arrangement. In my case, it may have been a way to compensate for the limited functionality of my aquastat.

A couple quick questions for you (I don't think we asked them yet)...
How old is the boiler?
What fuel type is it (oil, gas, wood, etc)?
When was the last time you had it serviced and/or cleaned?

I would consider the info provided by NJ Trooper. Although not particularly fimilar with over seas setups, he's a really knowledgeable guy and has helped me out many, many times with my boiler when I first joined the site.

If the expansion tank is not the issue (sounds pretty likely to me personally), my next obvious thought would be the aquastat.
 
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Old 04-19-13, 08:54 AM
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Boiler is 8yrs old.
It burns Kerosene Oil
Last service was (embarrassingly) ~6yrs ago.
 
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Old 04-19-13, 09:39 AM
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Time to have that bad boy cleaned and inspected.

You'll probably notice a difference in your heating cost after the fact.
 
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Old 04-19-13, 03:40 PM
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Its a fully pumped system
So you are saying that you have a tank in the attic ?

Is there an expansion vessel on a non-sealed system?
There doesn't need to be, but I believe there is one built into your boiler.

my system is a fully pumped (non-sealed) setup with separate pumps for underfloor heating, hot water, & rad heating.
If you are basing your statement of this being a fully pumped (non-sealed) system on the fact that there are pumps, then this assumption could be mistaken.

Please tell us why you believe that this system qualifies as a "non-sealed" system.
 
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Old 04-22-13, 02:24 AM
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There is a small tank in the attic which keeps the circulating water topped up, there is no pressure gauge in the system. The boiler itself (50/90 boiler-house model) has no expansion vessel and I don't believe there is an expansion vessel anywhere else. These lead me to believe it is a non-sealed system.

I will have a boiler specialist come take a look at the boiler but the aquastat arrangement still troubles me. The fact that a pump can turn on without the boiler firing and that the boiler can fire with no pump running seems crazy. Two completely independent systems which are supposed to co-operate as if by magic to heat my house & water. I would be much happier if the boiler firing was linked to pumps running.
 
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Old 04-22-13, 04:55 AM
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What is your exact model, as some have timers and means for DHW production.
Does your expansion vessel, Attic mounted... have an auto refill system to it ?
If so, it might be not sealing off fully.
Do you know what temp the boiler gets to ?
Does it shut off on high limit ?
have you tried adjusting the boiler aquastat ?
 
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Old 04-22-13, 03:31 PM
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The exact model is Grant EuroFlame 50/90 Boilerhouse.
The small attic tank has a ball **** refill system. The overflow from the heating dumps into this tank also (generally causing it to spew water out through its overflow pipe).
The limit stat on the boiler is 110C, it hits this if no pump is running.
The control stat (which I replaced) I have set to the lowest; 60C which it cycles above/below so long as there is a pump running.

I had a look at my 'system controller' today (grey plastic box in the utility room with all the wires from stats, pumps etc going into it) hoping to find a jammed relay or burnt transistor (I'm an electronics engineer by trade, can fix most electrical things). What I found instead was a birds nest of wires. No controller, just hand wired connections from AC mains to stats to pumps to boiler. The bandit electrician who installed my 'system' assured me it was intelligent, adaptive, reliable etc etc.
That said it didn't look like anything was disconnected or shorted so I guess the overheating problem really IS with the boiler.
I've called a boiler guy, he'll come to have a look in another day or two. But in my heart I know that if I waded in and rewired the 'controller' so that the boiler only fired when a pump was running it would not overheat. It has been some years since the boilers last service so I guess I owe it.
 
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Old 04-22-13, 08:41 PM
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Yes, you do owe it one.
The system should be able to cycle on the adjustable aquastat even with out a pump. It's not the best way to do things of course.
Has ANYTHING changed in the system, fuel, surroundings recently that times coincedentaly with the boiler acting up ?
 
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Old 05-15-13, 01:39 AM
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Update on this.
I called a boiler guy, he reckoned a boiler servicing would fix the problem. He came, he serviced, he changed: the nozzle, fire valve, oil hose, photo cell.
There is no doubt all this needed doing but it has done nothing for my overheat problem, very next evening the limit stat tripped again.
Boiler guy reckons what I need is a pump over-run based on a pipe stat (so that hot water doesn't hang around in the boiler after the heating stats have been satisfied). I don't believe this is the problem, I'm pretty sure the boiler is overheating while one of the pumps is running (I've got three pumps: underfloor heat / upstairs rads / hot water ). My suspicion is that one of the pumps (the underfloor one) is not moving water out of the boiler efficiently enough, maybe due to blockage or just worn pump. I'm going to spend a few evenings running each pump individually to check this theory out. Anyone have any thoughts on this ?
 
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