Hot water issues on indirect unvented system

[craigy]

Hi all,
the system involved is a sealed y plan, indirect unvented cyl heated by a Raeburn fuelled by NG.
the stat on the cyl is calling and the pump kicks in, boiler fires up and the temp rises to 40 degrees in 15 mins or so, then the boiler cuts out, and does not need resetting. This happens when on both h/w only and c/h & h/w settings on the boiler. The c/h stat is calling and the sequence repeats with the motorise valve rotating anti clockwise, but only about 45 degrees, and at resting position the manual override arm is slack from far left to the middle of the slot, the only resistance felt is when reaching the locking position. There is a manual bypass fitted with a gate valve after the pump connected back into the coil return.
The high limit stat was removed when I arrived dangling by its flex. The PRV &TRV combined valve was not operating when tried. It was fitted external to the cylinder via 15mm copper, I thought it had to be threaded directly to the cylinder?
so my thoughts are replace PRV/TRV, high limit stat, 3 port valve.
any thoughts or suggestions welcome thanks in advance

 

[AWheating]

Is the zone valve opening after the 3 port valve on the hot water side? And is there correct circulation?
It sounds like the set up is quite old and has never been serviced. Bring it up to spec, do all the safety checks etc..... do not leave working until it's all safe and correct.

I assume you are g3 qualified? ( got to ask for safety reasons )

 

[cr0ft]

no offence but are you actually qualified to work on these cylinders? I am only asking as your thoughts strongly suggest you aren't. The current setup is dangerous and if you can't identify why you shouldn't be working on it..

 

[craigy]

no offence but are you actually qualified to work on these cylinders? I am only asking as your thoughts strongly suggest you aren't. The current setup is dangerous and if you can't identify why you shouldn't be working on it..

Did you read the post till the end?

 

[PlumbBobBob]

yes we read the post to the end and you haven't answered the question

 

[plumben]

I guess you isolated the supply to the cylinder and told the customer not to use it until you carry out the repair works?

 

[craigy]

I have my unvented qualification yes

 

[craigy]

I appreciate your concerns for safety reasons, you have your question answered.
Many thanks

 

[cr0ft]

Then it worries me a bit that you say this: -

so my thoughts are replace PRV/TRV, high limit stat, 3 port valve.
any thoughts or suggestions welcome thanks in advance

You cannot have an unvented cylinder installed on a Y-Plan system (unless you also fit the supplied 2 port zone valve after the mid position valve on the pipe run to the HW coil). mid position valves can and do fail in the hot water on position which would cause the cylinder to overheat dangerously if hot water was selected at the programmer.

If you had done your G3 course you would certainly have been made aware of this..

 

[WaterTight]

stick in a fluidmaster. never fails.