Worcester 350 Combi Intermittent Shutdown and Restart

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Gloucestershire
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Hi,

Our Worcester 350 boiler has been shutting down fully over the last few days and then restarting itself....

- All panel lights go out, including the controller display.

- I've not needed to press the overheat reset button on the top.

- Pressure is 1 bar - not changed, no low pressure light (which from memory doesn't cause the controller to power off).

It is not clear how long it stays 'off', but it powers up again itself.

As the controller clock resets, I think there were a few resets after maybe 15mins of running ch+dhw.

Last night, I caught it in a completely off state - switching the power off/on did not bring it back to life. Tried this again a few minutes later (after checking the mains fuse), and it was working again.

Trying some diagnostics today:
- full dhw and no ch appears okay
- dhw switches on/off as expected
- ch on with lowest temperature is running okay.

Not yet tried max ch and then using dhw as well - as it is running, I'd like a warmer house and a shower.

There are a bunch of posts re the overheat reset button, but mine has not tripped. Is there anything else I can sensibly test before calling out an RGI?

I've got the cover off, but don't want to touch the combustion chamber.


(Given the controller clock resets, but not the ch presets then the CH side is a PITA - I see there is a hack to add nicads to keep the clock ;)
 
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Hmmm - completely died now.

Yesterday it was fine after running the central heating on max for a few hours, and filling a couple of baths. It restarted itself about 15 minutes after one bath (the CH was on as well).

Stayed off for 6 minutes before the standby light came on by itself.

This morning it has shutdown again - this time during using a shower for 5 minutes. The ch has not been used for 8 hours.

There is power to the driver pcb and to the low pressure switch (X7). The next step in the manual is check for live supply on both pins of X9 (the overheat thermostat).

No power there - pull off the plug, check between the pins and between each pin and gnd - nothing.

No resistance between the pins of the overheat thermostat lead - this is probably correct - if it tripped, then I'd expect open circuit to cut the power.


Driver board? Or is there some other sensor that has tripped out?


WB engineer or normal RGI? Looks like a WB-specific fault to me...
 
Any competent boiler engineer should be able to find a fault on your simple boiler.

But many who do installs will be trying to tell you it should be replaced.

Ignore them because it is quite repairable but just needs someone who does repairs and not just uses repair calls to get installation jobs!

It is getting on though!

Tony
 
Progress...

Came back after a few days away when the boiler was switched off.

Switched on - low pressure light.

Odd, as that hadn't happened prior, and pressure on dial is 1 bar (and goes up when I added more water).

After following the wiring on the back of the driver board, re-reading the diagnostics, and this thread:

//www.diynot.com/forums/viewtopic.php?t=254211


It is the low pressure switch - proved by swapping green/white - now all working.

I think either the microswitch internals are knackered or it is a bad design.

In the intermittent failure I had - with no low pressure warning - it looks the like the switch failed to power either white or green output.

Off to buy a new switch.

Can I run the boiler if I monitor the dial? e.g. can my wife have a shower whilst I watch the dial, just using dhw?


The dial is connected to a separate ch pipe than the low pressure switch - I think the expansion tank gubbins is between the two - i.e. flow and return.
 
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The official answer is no and that you have bypassed a safety device.

Many boilers dont have a LP switch though.

Tony
 
The switch on those models are prone to getting a bit of muck in the end all that is usually required is to remove and clean it out (after isolating from electrics and draining boiler)
 
Ta - yes it was just a low pressure switch full of 16 years worth of cack.

The diagnostic flow in the manual makes complete sense in hindsight - if no power to either green or white wire on the driver board from the switch, and there is power to brown, then the switch is fecked.

Think the PRV is now leaking after refitting - pressurised up to 2.5 bar to check for leaks, then used the PRV to get back down to 1.3.

Drip drip drip from the pipe - probably more cack stopping it seal properly (leaks enough to get back to low pressure state overnight).

A job for tomorrow - at least the isol valves have stopped dripping.
 
Drip drip drip from the pipe - probably more cack stopping it seal properly (leaks enough to get back to low pressure state overnight).

A job for tomorrow - at least the isol valves have stopped dripping.

Cack in the PRV is the usual cause of them failing to seat, but be wary of operating the boiler isolation valves. That same cack can wreck the 'o'ring seals on their shafts, and at your boiler's age they may crack/split/fail and cause more dripping. If you can get away with it close any auto-air vents and use the PRV to drain the system to zero pressure, then change the PRV quickly.

And to do it properly fully drain before the repair, introduce a sludge cleaner (X400 or similar) on refill to clear out some of the cack before redraining and refilling with a corrosion inhibitor (X100, MB1, etc)

MM
 
I'll take your advice on not touching the isol valves - if they start leaking, then some hefty kitchen redecorating will be required :(

Draining properly is no problem and much lower risk....

Is there any chance that the X400 could dislodge more cack that will end up in the boiler blocking something or other?

I'd rather cope with a failed boiler in summer than winter - I'm thinking that I'd fix the PRV and check for soundness over the winter, and do the X400/inhibitor when/if it ever gets warm again.
 

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