boiler overheating????

[barny3565]

hi ..hope anyone can help?
i have myson apollo 30/50.....which works fine when using it for HW..when i use it for CH..it fires up ok..all rads get hot...but when boiler stops flaring up...pilot goes out....just had new thermocouple and over heating stat fitted.....but still doing it..pump seems to be fine...because all rads are hot....but i,m no expert so only presuming....pump only 4yrs old.
bit of noise in system sounds like slight airlock...could that be it?...but like i said all rads hot enough.
to relight pilot...have to wait 15/20 mins..as if it needs to cool down b4 relighting.
only 2 settings on boiler....HI and LOW....
can anyone help, i,m stuck for wat to try next...tx

 

[Softus]

Haven't you posted this question somewhere else barny?

 

[barny3565]

have posted b4 but not sorted problem out yet.....really like some help on this 1

 

[Softus]

But have you still got two topics open on the same subject?

 

[Slugbabydotcom]

Firstly make sure the pilot flame is strong, blue and reaches the thermocouple ok. The burners or top sockets as they are known often corrode and the injector may be blocked

Need to look at why the limit stat is cutting out then seeing as you have renewed it.
It cuts out because the water it is sensing is to hot.
Some of most common reasons are

Pump overrun stat not working properly. This circulates water through the heat exchanger after the burner has stopped. If the pump goes off straight away when the flame goes out the residual heat in the HE will cause an overheat situation

Temp sensor--- Hi or lo stat not cutting the boiler off early enough.

Slow flow of water through the heat exchanger caused by a failing pump or because the pumps work is too hard - obstruction or more often sludge

Another thing with apollos is that the flow to return temp difference of 11ºC is quite important. This is controlled by careful adjustment of the by-pass valve. The idea is that by short circuiting the hot water directly back to the boiler then the water does not go through too much of a temperature change on each pass of the boiler. Open it too far and your radiators dont get hot. Dont open it enough and you will get 'kettling'

 

[barny3565]

hi slug
sttill not sorted my problem, i,ve been away and just got back....i,ve ran the boiler on LOW setting and it was fine.....the pilot didnt go out...and the same when i use it for HW......does this indicate it could be the HI stat that needs replacing??????
thanks slug

 

[barny3565]

hi slug
sttill not sorted my problem, i,ve been away and just got back....i,ve ran the boiler on LOW setting and it was fine.....the pilot didnt go out...and the same when i use it for HW......does this indicate it could be the HI stat that needs replacing??????
thanks slug

if there was sludge in the system, would heating still work ok on LOW, which it is doing???

 

[barny3565]

hi slug
if there was sludge in the system, would heating still work ok on LOW, which it is doing???

i have slight airlock noise in top rad in house, when heating is on....and another vibrating noise when running hot water......would rads still get hot if there was a blokage or air lock???.....they all get hot..
tx for any help u can give

 

[Slugbabydotcom]

For the cost of a high stat its worth replacing by way of elimination although I do feel that it is the culprit here..
I tell people to run their boilers on as low a setting as they can get away with anyway for economy and safety reasons.
So fit a high stat then dont use it

If all rads get hot all over their surface then your system is fine.

Bleed the top radiator when the system is turned off

Noise is water hammer [resonance] coming from the rising main feeding your hot water storage cistern. a.k.a. Cold pipe going to the big tank in the loft
Fitting a new float operated valve, a.k.a. ballcock ...... should sort it! Clipping loose pipework helps too

 

[barny3565]

have ordered a high stat, and will have it fitted as soon as, will let u know how it goes.
another question slug plz.
i,m running my CH on LOW at moment and although it doesnt go out( like on HI).....i find that it takes a long time to get quite hot and even tho room stat up to nearly 25.....its not that hot.....i think i would find it difficult to run on LOW when its really cold..
i,ve had boiler 16 yrs and never run it on LOW before now....
thanks for your help so far

 

[Slugbabydotcom]

Looks as though you need the high then!
The high and low switch/stats control the temperature of the water in your system. On other boilers a stat gives you variable control over this.

Low = Safer operating temp as regards scalding, plus the boiler isnt working near its limit.
Also its more efficient, as the hotter something is the more heat it has to lose, the more it loses it and the more you have to pay for that heat.

Benfefit of high is that the system reaches full temperature sooner.

If you dont have the required end product ie. a warm house. Then its got to go on high

 

[barny3565]

hi slug
i,ve had a new HI stat fitted and my boiler is still overheating resulting in pilot shutting off, i,m running out of solutions hope u can help me.thanxs

 

[Slugbabydotcom]

I mentioned most of the things that go wrong in my 5th post on this topic.

have to wait 15/20 mins..as if it needs to cool down b4 relighting.

Pump over-run stat is next on the list. Make sure you isolate all the electric to the boiler before renewing this. Check its function first though. It should keep the pump running for a while after the boiler has shutdown.

How long after the boiler has shut down does it take for the pilot to go out?

I'm assuming your boiler is the balanced or conventional flue version, that it has been serviced ie. the flue is clear, the heat exchanger is not covered with debris or blocked. The pilot flame is strong and plays properly on the thermocouple.

 

[barny3565]

the pilot light goes out a couple of minutes after boiler as stopped.....i,m not sure if pump is still running after, it works ok on LOW....i,ve turned my pump up to number 3 on settings.....my heating system seems to be running better now...warmer quicker.
but pilot still going out using HI.
i,ll try and get pump over run stat checked out
thanx......will let u know

 

[barny3565]

hi slug
i,ve just replaced my pump and its made no difference, the boiler still cutting out on HI,....i,m waiting for a new pump overun stat....i,m just praying its this because i,m all out of ideas.
in the summer i had 2 radiators off for decorating.....after they were put back on.....my other rads seemed to be out of balance, so i balanced them up so they were working ok...could this have anything to do with the boiler overheating problem??.maybe its started cutting out since they were off??
why doesnt my boiler cut out on LOW....is it because its not as hot???
thanks for your help slug