myson appollo taking off...help please

[graybabe]

Hi, I have a myson apollo that has a switch with high and low. when on low (30k btu) it runs smooth, when on high (60k btu) it runs smooth for between 15 and 20 minutes than sounds like its going to take off. banging and clanking until it eventually turns off. The pump is working and soinning and Ive cleaned and flushed the system. Its getting cold and im desperate for some heat in my house,can anyone help?

 

[sime10]

Have you got a bypass are all your rad Trvs's ?

 

[corgiman]

what is soinning?

reckon your pump has gone or you have an airlock

 

[graybabe]

Thanks so much for supper quick replies. 'soinning' should read spinning. No trv,s its an old system. sorry to sound thick but i dont know anything about a bypass. if it is an air lock how do I get rid? you can hear the pump changing speed if I adjust it so i feel it isnt the problem? what do you think?

 

[corgiman]

well the boiler is boiling so it aint circulating

either air or the pump

 

[graybabe]

thanks for that.how do i get rid of an air lock? Also if i bleed the rads ive noticed they need bleeding agin after a short space of time. can the system be drawing in air?

 

[corgiman]

do you have water in the small tank in the loft?

 

[graybabe]

the small tank is directly above the boiler in the cupboard and has water in it.

 

[garethgas]

Hi
Try running it on the low setting. Low =30kW High = 60kW is simply not true I'm afraid...its purely a temperature thing.
The most common reason for this is a combination of age and the blocking of the heat exchanger.
Without being there....its hard to say for sure...some on this forum will stab at a guess on this or that sensor/stat....but the reallity is...the most likely cause is scaling up of the heat exchanger.
A good way to see if I'm right is to try running it on the low setting and see if it's quieter. If it is, then is a safe bet that its the heat exchanger.
There can be other reasons, yes, but this is by far the most likely.
Hope this helps

 

[corgiman]

true

is any heat making it to the diverter valve??

 

[graybabe]

Many thanks. It works perfect on the low setting.
If it is the heat exchanger and ive used fernox does it mean the boiler is goosed?

 

[corgiman]

well I will pack up my multi meter

good call gareth

 

[Slugbabydotcom]

Hi limit stat, over-run stat or maybe someone closed the bypass valve

 

[namsag]

The apollo has 2 seperate stats for Hi and Lo . It is not uncommon for one of these to go and your symptons are classic Hi stat failure it is getting too hot, before the additional high limit stat trips boiler out till it cools down enough to come back on

 

[nickso]

The apollo has 2 seperate stats for Hi and Lo . It is not uncommon for one of these to go and your symptons are classic Hi stat failure it is getting too hot, before the additional high limit stat trips boiler out till it cools down enough to come back on

sounds like classic high stat failure to me as well