Ravenheat boiler not cutting off.

[Whiting666]

Hi we have a ravenheat csi/he range.
Keeps cutting off due to over heating. With some tweaking of radiator flows etc we have managed to reduce it cutting out. But it seems to constantly run without switching off to circulate the water when it reaches temp. Have turned the dial to minimum but continues to heat.
The radiators get very hot, despite the trvs.
Have replaced the overheat thermostat.
Pump seems to be circulating fine.
Help!!

 

[Agile]

Well there are many checks that a boiler engineer would be making but part from checking the flow rate there is little a DIYer can do.

What is the temp differential across the boiler on heating?

Tony

 

[Whiting666]

Sorry, I was a bit hasty with my post, it does appear to be cutting off, but does seem to be getting far too hot then shut off with overheat light. The ch dial is turned quite low and this helps, but turn it to optimum level or higher it shuts off. (Always used to be fine on this setting) seems to be heating higher than it used to.
Have been having this prob or a while but isn't as frequent unless its very cold outside.
All seemed to point to the overheat thermostat, but have changed that and still a problem.
When it was snowing we had a day of it cutting off every 15 mins.
Thought maybe the condense pipe could be frozen, but does do it when it's not freezing.
Fiddling with the trvs seems to slow the frequency down.
Also confused how the radiators get so hot with he trv turned quite low.

Sorry if its a bit jumbled info

 

[dcawkwell]

Boiler thermostat.

 

[Slugbabydotcom]

No1 suspect -
CH thermistor on the right hand side. It's either clip on or wet pocket. If its clip on give it a wiggle, make sure it had good clean contact with the copper flow pipe, perhaps clean off sensor and pipe and reapply a micro thin smear of thermal paste, check connections.
If it's wet pocket it may need replacing. Don't try replacing it if the boiler has been on in the last hour [a lesson I learnt the hard way] or if you're not sure what you're doing.

It's as if it's not sensing the temp properly because in case of a clip on its not making a good contact with the pipe ... or wet sensor because its coated with system debris

If you know how to test resistance it is usually about 9kΩ at room temp

After that you are indeed in need of a gas safe registered engineer. Possibly a gas valve needs professional adjustment/ replacement.

 

[Agile]

If you know how to test resistance it is usually about 9kΩ at room temp

Are they not common 10k thermistors? Or is your room quite warm?

Tony

 

[Slugbabydotcom]

Warm room! 9k - 10k we're still kicking a ball in the same field.
Usually about 7k if I stick it under my armpit for 10 mins
.

 

[Whiting666]

Thanks Agile, will give it a try later. Fingers crossed its that simple .

 

[Agile]

But I seem to remember that some Ravenheat sensors were 25k presumably just to "be different" .

Tony

 

[Slugbabydotcom]