Myson Apollo - Overheat on High Stat

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Hi,

I have a myson Apollo boiler which i presume is at least 15 years old, it has a 3 position thermostat (Off, Low and High). Ever since we have moved into the house approx2.5 years I have not been able to run the boiler on High, hence the heating is a little limp.

The boiler will fire, and react to the room stats and HW stats, but when set to high it will heat for ages and then shows no sign of cutting out - eventually banging and blowing itself out. i then have to relight and start again.... None of this happens on low setting.

It is connected to a 3 port valve, and is fully pumped.

From reading posts I presumed that it was related to a bloackage or poor flow rate, I therefore employeed the services of a powerflush, I also replaced at the same time the pump and HW cylinder stat. this made little difference, so I recently had the boiler serviced. The bloke did the service and i mentioned this issue and he said it's just the age of the boiler and it gets furred up and much more difficult to run on High.

On my suggestion he also changed the high stat, just to eliminate one more thing.

It still seems to get very hot (on high) and I am not brave enough to wait for it to boil over an knock out.

I suppose my question should be, shall I just get over it and leave it on low, or persue getting it working on high? Is this just a trait of having an old boiler.

I am sure I have missed something out, but who knows what - help me....
 
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common problem. usually the stat thats faulty

did he bother to check what temp the high stat actually cuts off at? if the heat exchanger is clogged you could be in trouble as they are obsolete.

put it on high and see if it starts banging again, only way to find out for sure if he's fixed it.
 
I have been brave, and the over heat temp seems to cut the boiler out eventually(but no banging!!). So i have to relight boiler.

What I cannot fathom is why the newly instaled high thermostat does not turn the boiler off..... Even if the circulation is a little poor why does the thermostat not cut the boiler out? If it is getting hot why not deactivate the boiler..... very strange. teh pump seems to be running all the time... After i shut off there was what sounded like running water in the boiler pipes...

Now wish i had swapped my degree to a corgi qual.
 
Now wish i had swapped my degree to a corgi qual...................Ah yes, the educated poor, this country is full of them............ :LOL:

With a low water content boiler like the Apollo, the water circulation is very important, so the system by-pass should be checked & ensure there's enough pipe between the by-pass & the circulator.

It's normal to fit both the Hi & Lo thermostats, not just one or the other. But a furred up HX could well be your problem.
 
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I have been brave, and the over heat temp seems to cut the boiler out eventually(but no banging!!). So i have to relight boiler.

What I cannot fathom is why the newly instaled high thermostat does not turn the boiler off..... Even if the circulation is a little poor why does the thermostat not cut the boiler out? If it is getting hot why not deactivate the boiler..... very strange. teh pump seems to be running all the time... After i shut off there was what sounded like running water in the boiler pipes...

Now wish i had swapped my degree to a corgi qual.

if its now cutting off the burner properly but tripping the pilot interruptor then i'd be looking to check the temp at the interruptor. if its under the magic 82 degrees and the interruptor has tripped you need a new interruptor.
 

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