Worcester 350...overheat pops after hot water run for some t

[currybum]

Hi All,

First post, so please be gentle. My faithful Worcester 350 has started to knock out the overheat button. This only happens after running the hot water for a long time e.g. bath / shower. It's fine on central heating.

Looking at the instructions, looks like overun should keep the fan ( or perhaps fan + CH pump ) running for 2.5 mins. I can hear than fan run for approx 5 seconds, then the overheat pops out, leaving boiler dead with no lights.
When the boiler cools down, i reset the overheat, and the fan ( sounds like fan ) does indeed run for 2.5 mins.

Any advice welcome ( electrical only as wouldn't touch gas )!

Seem to be hearing different opinions from plumbers cover a faulty pump, central heat sensor, blocked heat exchanger driver board. I could spend a fortune getting to the root cause!

Cheers, Currybum

 

[Agile]

I thought that only the pump is over run. Does that happen?

Regardless I think that the over run stat is inside the combustion chamber which should only be accessed by the gas registered.

Others might confirm that but you may be able to see in the service manual.

Tony

 

[currybum]

Thanks Agile for that fast response. Well, things haver actually moved on since my last post. Now, the overheat is popping WHEN running hot water for several minutes ( as opposed to after running the water ).

Does this help narrow down the Issue e.g. could it be the central heating sensor, or hot water sensor thats faulty?

Cheers, Currybum

 

[spraggo]

Hi All,

First post, so please be gentle. My faithful Worcester 350 has started to knock out the overheat button. This only happens after running the hot water for a long time e.g. bath / shower. It's fine on central heating.
Any advice welcome ( electrical only as wouldn't touch gas )!
Cheers, Currybum

Your boiler contains two pumps, one for central heating and one for hot water and your symtoms indicate that the hot water pump is faulty, ei, not running at full speed.

spraggo

 

[Agile]

I would expect the pump IS running if you are actually getting hot water.

I suggest you check that and if so that you measure the resistance of both sensors?with the boiler cold. I think they should be 13 k but it might be 1.3

Tony

 

[currybum]

Thank you - yes, the HW is working OK and is a good temperature. The boiler is now inter failing ( overheat stat ) 1/2 way through a shower, or 5 seconds after finishing a shower.

I'll measure the sensor resistances as suggested.

Cheers, Currybum

 

[Andygasman2010]

I'd suspect one of the heat exchangers is partially blocked. Have an RGI check the burner is modulating properly first though.

 

[currybum]

Thank you for opinions - most useful.

I've had the central heating sensor changed - the old one was falling apart on the terminals. Unfortunately, the fault is still on i.e. C/H works OK, but hot water causes an overheat in less than 2 mins. Seems to be getting worse.

My Gas Safe mate is attending tonight and I guess will diagnose a faulty hot water pump, or a blocked heat exchanger?

Will share the outcome in this thread.

Cheers Currybum

 

[currybum]

Update: water pump was tired and has been changed. Also automatic air vent.

My expansion tank diaphragm is faulty, as was leaking water when valve pressed.

Still cutting out after running Hot Water, so cleaning solution applied. New hot water manifold on order also expansion tank.

All adding up, but cheaper than a new boiler!

 

[currybum]

Oh dear. DHW exchanger and expansion vessel both need changing ( £245 for parts ).

Friend suggested use Worcester for a fixed price repair (£215 inc VAT ).

Called Worcester who say 350 is obsolete, so won't come out!

Looks like I will have to get my local plumber back out to change the parts.

 

[onlyfitidealboilers]

he wont want to do that!!!!!!!

 

[currybum]

Update:
expansion tank, DHW exchanger + overheat stat changed.

System now running like a dream. Now, if this baby can give me another 5 years, that will delay the pain of shelling out on a new 37CDi

Thank you for everyones help.

 

[Agile]

Now after changing all those parts, which ONE part was responsible for the boiler failing?

I have a feeling that a thermal survey would have identified just the one part although the expansion vessel would have needed changing ( or a cheaper external one fitted.)

Tony