Very hot water problem on Worcester 28i

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Hi all,

I'm having a bit of trouble with my boiler, a Worcester 28i RSF.

The hot water has been intermittently running really hot (up to 85degC) and tripping out the overheat thermostat (requiring the reset button to be pressed on the top of the boiler).

This happens a up to 5 times a day at the moment. It's difficult to tell the exact actions that result in the trip, but it seems to be mostly when a tap is running (very) hot water and then the hot water demand is reduced by either turning the hot water tap down/off, or adjusting a mixer tap to cool the flow.

There is no temperature control on the 28i so nothing to adjust, I believe the maximum output temp for the unit is set at 55degC.
There is a good strong flow and I haven't noticed any drop off since the issue started occurring.

I have replaced the DHW thermistor with no effect.

I called out a plumber who didn't know what the issue was, but after a few calls to the Worcester helpline he suggested that the PCB probably needed changing, but can't say I was overly convinced.

The other thing I thought may be the issue is the flow turbine.

Before I have a go at changing either of these parts, is there anything else I could check?
And if not, which do you think is the most likely culprit out of the flow turbine and the PCB?

Many thanks,

Andy
 
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R u sure its the rsf ? I've been to one of these today and it definitely had a dhw temp control (and no flow turbine)
 
R u sure its the rsf ? I've been to one of these today and it definitely had a dhw temp control (and no flow turbine)

You sure gigz. I'm pretty sure they don't have a dhw temp control? And pretty sure they have a flow turbine too? Maybe your thinking of the cdi rsf?

Op. We can't give diy gas advice on here. But if it is the part I think it is then it may be cheaper for you to call Worcester for a fixed price repair
 
Last edited:
Yeah, my bad, it was the CDI (y)
 
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Cheers, I'll give Worcester a ring.

To be honest I'm half thinking of just getting a new one installed. Over the last year, despite it being serviced, it's started to make some horrible noises at times and regularly looses water pressure.
I assume the fixed price repair would just cover one set of symptoms a time rather solving them all at once?
 
I had the same type of problems on a 24i.
Easiest thing to check is whether pump is set to max
Next is whether the pressure vessel is charged
there is a pipe on the 24i inside the boiler, not combustion area, quite thin which is a bypass pipe which is supposed to let hot water escape so that the overheat trip out doesn't operate this pipe is narrow bore and can become blocked. If you look at worcesters web site they used to do a parts cat for their boilers so you can see a breakdown of what goes where.
Swop the thermistors over they are the same for heating and hot water, I know you have changed one already but it doesn't mean its good.
Lastly its a pcb change, fiddly but it can be done. Ebay it.
if the prv has been letting by you can bet it wont seal properly again so I'd change that as well
 
I don't see that this is going to be anything very difficult to diagnose. But it will need an engineer capable of proper fault diagnosis including being fully conversant with gas valve settings. I find that surprisingly few are.

Tony
 

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