Greenstar. Ideal for lobster cooking or ice in your Martini.

[JohnHuson]

Known this boiler 24i for years. Gas safe certificate every year. Here is history over last few weeks; That engineer has been out but is intent on
replacing 'all sensors' and going down the parts list until solved.
Nice Fella though!
Output starts very hot then goes cold on DHW supply, particularly bath and shower. Can go OK for 2 minutes to 5 minutes then go cold, boiler shuts down.
Suspected gunge in system, so introduced suitable chemicals for a few days.
No difference. Boiler not in limescale problem area.
Diverter valve seems ok. Boiler ignites OK. Pressure OK but not checked expansion vessel pressure.
Boiler continued with hot and cold routine.
Changed Thermistor for new one. Seemed OK overnight but now getting very hot then shutting down. However...…..if the shower or bath supply is
quickly adjusted so that it does not have chance to get very hot by introducing cold water it can go long enough for normal bathroom use.
My logic? If it can run OK with water temperature controlled to acceptable level by balancing cold water output then that eliminates water flow sensor, thermistor, and what else?
Your help appreciated please, Cheers, John. (shaken not stirred).

 

[JohnHuson]

Its a Junior. It now seems that if the bath cold tap is turned on first to a small flow then the hot tap on, it will then maintain an acceptable temperature for a shower and good delivery of water.

 

[Gasguru]

Sensors are generally bulletproof on these models.
I suppose the turbine could be failing but that can be checked with a multimeter.
A blocked plate or weak pump would be a starting point and it's a 2 min job to diagnose...limescale is irelevant.
Injecting chemicals...I have my doubts whether it would clear a serious blockage.
Main hex can block on the connections.
Pulling the plate out's a PITA job on these.
I'd be looking for someone else or pay £££ and get Worcester out.

 

[martyndc88]

Sounds like a blocked plate hex to me

 

[JohnHuson]

Thanks for your help everyone. More info on this for your views please;
If we turn up the DHW control knob to maximum and then turn on the cold supply at the bath a little, then
introduce the hot the supply can stay stable without shutting down.

If we reduce the DHW temp dial by half and operate the taps as normal then again the warm water supply is stable.
If we increase that temperature to 80% the water gets hotter but starts to vary in the hotter supply temperature, but does not shut down.

The volume of that water is good so eliminating the HEX possibility?
What is it that controls the DHW temperature via the control knob on the panel? Could this be the gremlin?

 

[martyndc88]

How old is the boiler? Does it have an on/off button?

 

[kidgreen61]

As said earlier, it will almost certainly be the plate hex needing cleaning.

If the boiler is piped from below, the hex is easily removed by cutting into the DHW pipe and removing the top 6" or so, allowing room to get plate out.

Not so easy if piped from above.

 

[JohnHuson]

Thanks for the tip, much appreciated. Yes it is an old boiler and is due for replacement but trying to keep
it going until kitchen refurb.
Yes, it does have ON/OFF switch.
In removing part of the DHW pipe.....is this below the boiler area to allow for the removal of the DHW union
that restricts the job otherwise? I assume the connection from the bottom of the boiler wall plate to the HEX
is not removable to allow it to jiggle out?

Cheers, John.

 

[Gasguru]

You're straying into gas territory once you have the cover off these boilers...see the forum rules.
As said before get someone competent in or call out Worcester...you're heading for disaster if you're diy-ing.
Tests need doing before the effort of removing the plate is undertaken.

 

[JohnHuson]

I agree, and I would not consider touching the gas side, that is why I asked my Gas Safe man who does
the annual checks to do the job, but as I say on my opening comments that he changed the Thermistor
but it did not improve things.
Since then he has been busy, but was looking to order 'sensors' and replace them in succession until
the problem is solved. He will sort it out if the repair requires his expertise when I can diagnose the
repair required correctly.

As an engineer/landlord I have over many years repaired boilers on the non gas side with 5 inherited Worcester's
on the go at one stage. I managed to get shut of them eventually through unreliability. I finally gave up when I found a
PCB for £120 could be repaired by a qualified Electronics Engineer, with a capacitor from Maplins on the panel
for 90p plus his wage.

This Junior is due for replacement early next year when this tenant intends to move to a larger house and a
new kitchen is fitted. I am trying to keep it going until then.

The logic of this repair does seem to be as a result of the plate hex? I assume the hot is not flowing quick enough
through the plate so triggers the upper temp sensor. This is countered if the cold is turned on before DHW supply
and provides hot shower supply which is plentiful.

The tenant always firstly turned it to hot, then added cold, but it shut down within a couple of minutes from reduced
flow through the plate?

I appreciate the help you gentlemen give and respect the boundaries demanded by safety needs.

Cheers, John.

 

[JohnHuson]

Am considering ordering a replacement Vokera Easi Heat 25kw. I hope they are OK.

 

[Gasguru]

You need to find another rgi that knows what he's doing...I guess he's recommending the Vokera.
I don't get the logic in ripping out a boiler with the best spares availabilty and back up in the industry bar none.
They not the nicest to work on but the Juniors are robust and have few design faults.
Unless there's something fundamentally wrong (eg. a leaking primary heat exchanger, or it's rotten inside from poor servicing) it makes no sense changing the boiler.

 

[JohnHuson]

Thank you everyone, and you Gasguru.
I agree. Primary HEX is fine, no tell tale stains.
I will do what I can and look for another RGI instead of slapping new parts on it
until a cure is found.
Cheers, John.