Worcester 350 overheating! But is it really? Not thermostat

[nv_london]

Hi everybody,

I'd like to pick your brains and ask for advice on a central heating problem I have!

I've moved in to a property with a Worcester 350 combi boiler - it was working fine last winter, but this winter (and more specifically a few months ago), it completely and all of a sudden cut out. It was the overheat thermostat. After resetting it, it worked for a another day or so before the same thing happened again. I was advised by a friend to replace it (even tho I think it was working fine and only doing its job!). So I did replace it, but the same thing keeps happening, i.e. the boiler is fine and never overheats or cuts out if I only use hot water, but 15 mins to an hour after switching on the central heating the boiler cuts out.

I've had it serviced (everything was apparently fine, i.e the pumps were working and you can hear the central heating firing up and switching itself off) so I now use it with the thermostat unplugged! (I know this is a bad move, but it's so frustrating not being able to decipher the problem). I've been assured that the boiler itself is ok, so why does the thermostat (when plugged in) keep popping up and shutting the whole thing down?

Any suggestions or ideas would be greatly appreciated.

Many thanks,

John

 

[superdupergasman]

Could be a sluggish pump or more commonly on these boilers the primary thermistor located on the front of the main heat exchanger.

This tells the boiler how hot it is, if it has gone out of range the boiler me be firing at high gas even although it is up to temp.

Try checking with a multi meter to see what is resistance is when cold and hot to see if it is verying.

 

[nv_london]

Many thanks for your reply superdupergasman and you'll need to excuse my ignorance, but.....when you refer to the [primary thermistor located on the front of the main heat exchanger], could that also be known as/refered to as the central heating sensor?!? It's just that when I looked up the different components in the installation manual, I couldn't find a 'thermistor' just a 'central heating sensor' which was located on the heat exchanger.

Thanks for any help yet again.

John

P.S. if it is this, I think I'd rather just replace it straight off as they're not that expensive and I have no idea how to go about [checking it with a multi meter to see what is resistance is when cold and hot].[/quote]

 

[gas4you]

Firstly, don't use it with a safety device removed or disconnected

It is tripping for a reason, to protect YOU

Is the ch pump really working properly?

What is the colour/state of the ch system water?

 

[nv_london]

You're right when you say that it's tripping for a reason, but I'm not so sure that it's to protect me, at the moment it seems as though it's doing so do wind me up.

The repair man said that the pump is working fine (at the time, I didn't take too much notice of how he checked this or how he came to this conclusion) as I thought it would all be sorted and so just went along with what he said. However, since looking at other posts on this forum, I think another sign of the pump not working is that radiators far away from the boiler aren't heating up....but this isn't the case, all radiators even the furthest from the boiler all heat up and do so quite quickly (a matter of minutes).

Also, by reading these posts, I thought that the system may be sludged up and so I introduced X400 for 2 weeks before draining the system and flushing it a few times. The water was quite 'bitty' as in, it had lots of black particles in it. Since then, the boiler cut out and the 'low pressure' indicator light was constantly on even tho the pressure guage was showing a pressure of 1.2 bar....(in the end the repair man found that the water pressure switch was clogged up......probably due to all the crap floating around which X400 dislodged but which I didn't get rid of by draining and flushing). He got the system working by cleaning out this switch, but it still overheats and he still doesn't know why.

Could it be the dislodged sludge in the system slowing the whole thing down and making it overheat? or am I just clutching at straws on this?

Or could it be the thermistor/sensor?

Thanks for any help.

John

 

[gas4you]

Until you know the reason for the overheat tripping, any RGI worth his salt, or you for that matter, should always err on the side of caution and assume it is a safety problem until proved otherwise.

With WB boilers I always recommend a fixed price call out to WB themselves, includes up to 3 major parts.

 

[superdupergasman]

Yes I ment the cental heating thermistor.

I would re-connect overheat stat pronto and get the sensor changed, if problem persists get WB out to look.....Will cost you but you can sleep at night knowing your boiler will not explode or go into meltdown due to overheating

 

[nv_london]

Yeah, thanks Dave....while I agree that getting a WB engineer out is the best and probably most logical conclusion to this problem, I was hoping that the forum and it's members might have experience or alternative ideas to troubleshooting such a problem.

 

[gas4you]

Clf gas is one of our resident WB experts who may be able to advise better.

I for one have to admit that I don't know everything about boilers, especially WB, which as regulars on here will know that I cannot stand

This is the reason I personally advise calling in WB themselves to my customers if the fault is not obvious.

No one on here is perfect and knows everything , although some on here may like to think they do

 

[nv_london]

Thanks superduperman, I'll change the sensor and let you know how I get on.

(With regards to re-connecting the thermostat - I can do it......but after 30 mins my boiler will cut out and I'll have to re-set it, time and time again. In that case, maybe it really is time to bite the bullet and call out a WB engineer!).

 

[nv_london]

Thanks Dave. Believe me, after all this time, I'm not expecting miracles!

By the way, how do I get in touch with 'Clf gas'?

Thanks

John

 

[gas4you]

click on his name on another post and you will find his e-mail in his profile.

 

[superdupergasman]

you not getting the gist of how dangerous by-passing the overheat stat is!!!!

I have seen this done before and it melted the inside of a boiler out.

this stat is cutting out at between 90 - 100 degrees so it is obvoisly gettting up to this...so in your best interest....put on another jumper and switch off your boiler.

 

[corgiman]

Very well said superduper

 

[nv_london]

Believe me, I'm more than happy with wearing two or more jumpers and having cold showers, my girlfriend however, isn't! So while the boiler doesn't work I get serious earache.

I will however, aim to get it sorted, even if that means getting a WB engineer out.