OSO 20 RI Unvented Cylinder

[BournemouthPlumber]

Hi guys - went to customer today, pushing out boiling water through Temp relief valve, looks like cylinder stat isn't working as motorised valves both seem fine.

However, upon looking at the cylinder there didn't appear to be a high limit stat fitted anywhere - or any other means of electrical energy cut out.

Any ideas how they would have achieved it - if at all?

 

[Mr Smyth]

Don't know a great deal about unvented. But aren't the temp/pressure relief valves set at +90 degrees. Is it actually that hot??

That has always made me think that most of the time it is the pressure that causes the fault.

I am as much asking a question as trying to assist

 

[picasso]

looking at the instructions the high limit stat is fitted in series with the cylinder stat, it looks like one stat but its two separate things.

 

[transam]

Should be contained in the cylinder stat assembly ?? over heat shuts M.V ?

 

[BournemouthPlumber]

Thanks all...

@picasso many thanks - i didn't have these to hand as customer has lost them. Makes total sense they'd be as one as I couldn't work out why both of them had failed!... if its the same unit then that explains it.

MV is working as expected but Stat isnt shutting the MV off.

@Mr Smyth - to be honest i didn't stick a thermometer in it - but it was steaming and didn't even dare put my hand under it. Water from the taps was too hot to even get your had close too.

System has been left turned off until i can get replacement thermostat.

 

[mysteryman]

You should have an unvented certificate to work on these.

It could be a faulty pressure relief valve, or pressure reducing valve.

Please let us know what you find.

 

[BournemouthPlumber]

With all due respect I do have an unvented card

I was just asking a simple question as I didnt have the MI's and before going to have a proper look tomorrow and wondered whether anyone had experience with this model. I don't tend to work on or install the OSO's.

I called in on my way home this evening as they called in a panic to say that boiling water was pouring through the tundish.

I ran a couple of tests and PRV and TRV seem fine - MV is operating when switching between DHW and CH, however it is not operating when the cylinder gets up to temperature for the DHW - hence following the faulty stat train of thought.

 

[transam]

Could be that the high limit stat in housing has not been connected , eg by passed ?? & cylinder stat just been wired ? saw one awhile back were the electricians , had by-passed the immersion heater stat altogether !

 

[BournemouthPlumber]

Thats what I was worried about.

Main issue is the cylinder stat isnt working - but as i said, just an after thought that I couldn't spot a high limit stat anywhere obvious made me query a) where it was and b) why it hadn't cut out the boiler primary's before the TRV operated.

Will have a proper look tomorrow and trace it all back.

Cheers again guys for the constructive comments.

 

[kevplumb]

View media item 24863
talking of dodgy installs

 

[BournemouthPlumber]

About a year ago I went to quote for a commercial job on a retirement home - about 40 unventeds all down in the basement... id say 90% of them were rusted almost through.

Never got out of somewhere so quick in all my life! They had an "onsite maintenance man" who had been doing al the work to them over the years. No idea what he was doing or what he was dealing with.

You'd think the amount they charge their residents they'd be able to manage to run a decent plumbing/sanity system!

 

[Whitespirit66]

[quote="BournemouthPlumber";p="1694259You'd think the amount they charge their residents they'd be able to manage to run a decent plumbing/sanity system!

Did they all have dementia?

 

[BournemouthPlumber]

Knew i shouldn't post at 11pm!....