Burning smell from boiler

[jabberwok]

We were walking around the house with our noses in the air last night trying to track down the smell of a blown-out match. We found it was coming from the boiler.

We have a Worcester 240 RSF Combi with the following dials/switches available:
- temperature dial = minimum->max
- central heating timer = off/auto/constant
- hot water = off/on

With the hot water set to 'on' the boiler is constantly lit and it's during this time that the smell starts to build up. For this reason we only ever turn it on if we need hot water - very inconvenient. It's only started doing this in the last few days though.

We've also just recently been having problems with overheating (see post here: //www.diynot.com/forums/viewtopic.php?t=4916), and although that problem did stop for a while it has returned.

We'd be really grateful for some pointer on this as it's driving us up the wall with worry.

 

[jabberwok]

a quick update...i've just turned the whole thing off as I heard a pop inside the boiler when running the hot water tap.

am now draining the system - could air in the system be causing this?

 

[AnonymousImport]

This problem is not air as the boiler airs itself, provided the auto air vent is open. This is located inside the combustion chamber and has a cap like a car yyre valve make sure it is open half way. As Chris mentioned the last time the diverter valve could be jammed, do you get plenty of heat to the rads?

If you drain the boiler how black is the water?

The burning smell is the plstic parts in the boiler burning. If the boiler overheats again run it with the stats turmed down to disapate the heat. Only do this after you have left it for half an hour.

The heat exchanger in this boiler is a tin/copper one and is not that difficult to melt or burst.

I would contact a company that specialises in boiler repairs or worcester and get them to repair it before you melt a good boiler, this is not a job for diy. Sorry

If you have more info might be able to help more.

Gasman

 

[jabberwok]

hi gasman, thanks - doesn't sound good though.

first, in answer to your questions:
>Plenty of heat to rads?
- Yes, we did before turning the system off for safety - i'm afraid to turn it back on now!

>How black is the water.
Well, i've only drained the system via the radiators and the water was clear in all but one of them, and even then it wasn't too black.


i've opened up the boiler fully now to have a poke around inside and have discovered that a small leak is present underneath the diverter valve (the black block). I took the top of this block and got a strong whiff of tcp/match smoke, so we've found the smelling culprit. The water coming from this leak has spread all over the bottom of the boiler cabinet and into the electronics compartment - not a lot of water, but it's made a pretty mess.

Anyway, in an attempt to get all the air out, I drained the system via all the radiators (had a bit of fun when i turned the key too far and it blew the stoper out!), filled it back up again to 2.5bar, then drained it back to 1.5bar using the pressure release valve on the boiler. However, water is now constantly coming out of the overflow pipe even though i've turned the pressure release valve off again.

Does this help any further with diagnosis?

 

[AnonymousImport]

Give the press relief valve a few twists, it will make a clicking noise everytime. If this won't work try opening and letting water run past it a few times to clear any dirt. You will need to re-pressurise.

To air the boiler turn the stats off and switch the ch on to run the pump, you will hear the air gurgling round. Make sure the vent I told you about is open (it could be on top of the pump). If the boiler starts to light turn the ch off, do this a few times and the air should clear.

Gasman

 

[jabberwok]

Ok i'll try those suggestions now.

I've also attached a couple of pics of our boiler that may help. In the documentation it mentions that a sealed system should have the air vent cap removed and discarded, so i'm assuming that's been done before hand as the boiler's probably quite old and has been running fine until now.

 

[AnonymousImport]

The leak you describe is from the gland that seals the pin that makes the hot water flow switch. This part is only a few quid. Turn your not water tap on and off the pin should respond very quickly if not then the gland I spoke of comes in kit with a new diaphram and will probably need a change if you cannot get the gland alone. This leak is not the cause of your problems.

Another cause could be the ch sensor not telling the boiler to go off. If you have a multimeter check the resistance across this (power off!) in should be in the kilo ohms range. Do this with all the sensors in the boiler. Make sure you pull the wires carefully off first.

When you try to air the boiler you should hear hissing as the boiler airs itself.

Gasman

 

[jabberwok]

Unfortunately I don't have a multimeter to check the resistance across the wires you mention. Do you think the leaking part is not particularly dangerous then? could i safely run the boiler with it in that state? If i can at least use the central heating and not hot-water, then i'd be happy for the short term. Does this diverter valve microswitch have anything to do with the CH or is it just the water?

In the meantime, i've been trying to air the boiler using the method you describe:
- turn hot water to 'off'
- turn temperature dial to 'minimum'
- turn CH to 'constant'

Now, am i right in that I've filled the boiler with water up to 1.5bar before doing the above - or should it be completely empty? The overflow pipe is still expelling water before I've turned anything on and I've turned the PRV clockwise as far as it will go.

 

[jabberwok]

Incidently, when turning the hot water tap on/off, there is a small black disc on the diverter valve that moves back and forth. It does respond quickly to the tap going on/off, but takes about a second to move to where it needs to go.

 

[AnonymousImport]

You can run the boiler safetly this drip is mains cold water. If you have no problems with overheating with ch on then it will be ok to use it.

The prv turns anti clockwise (it only goes one way) and makes loud clonk when it seats again properl, it is spring loaded. By the way these valves leaking is not uncommon and it will have to be replaced. You will have to re-pressurise the system every time it drops below 0.2bar.

You will have to have the pressure to between 1 to 1.5 when airing. switch the central heating on leave it for a 20 to 30 seconds and then off again. You will hear gurgling as the air moves around. Repeat this a few times untill the air seems less you will know and then leave the ch running to dispell all the air. You should hear a hissing sound from the auto air vent I described ealier.


The diverter valve micro switch tells the boiler that there is a demand for hot water and is nothing to do with the ch.

I have just read all your posts again and if there is a strong burning smell from the micro switch there is a posibility that it has welded itself together. To check for this push the little lever and listen for a clicking noise.

Gasman

 

[jabberwok]

Thanks for all your help gasman - it seems things are looking up (fingers crossed)

The water running from the overflow has slowed right down and is now dripping once every second or so (hopefully this will slow down further, or at least until we organise a someone to fit a new valve). I switched the heating on and heard the gurgling as you suggested, ran it for about 20 mins to make sure it turned off when it reached the right temp. - which it did as i set it on 'min', but the radiators still got hotter than i would have expected on this setting.

However, i didn't hear a hissing noise from anywhere - i couldn't even find the air vent let alone hear it. I'm hoping that it did it's business without me noticing.

Once again, thanks to your helpful pointers for this novice-novice - the combination of gas, electricity & pressurised containers don't fill me with confidence!

 

[ChrisR]

The black box where the water's coming from has microswitches in it. If water gets into these it can make enough of a circuit for the boiler to think the HW is turned on. The boiler water is actually directed to the CH though, so the boiler thinks the HW isn't hot yet, so the radiators get hotter...

I think you can take the box apart (with the power OFF!) to have a butchers at what's got wet. A squirt of WD40 might be appropriate.

This sort of short tends to smell, too.

 

[jabberwok]

hello again chrisR.

So all the overheating problems could be caused by this small leak? Inside the box are two wires, the bedding screw of one of them has a rust-like residue around it. Behind the box on the valve itself there is a ring which also has this rusty residue. All the water seems to collect in this box as when i took the cover off it all fell out. Whereabouts should i apply the wd40, on the valve/wires or both? Would you suggest i get someone out to fix this, how much do you reckon i'm looking at?

Assuming we got the microswitch+valve fixed, there's still a problem with the overflow pipe - the dripping water never did slow down and when i woke up this morning the pressure had dropped right down to 0.5bar. I've turned the PRV several times as gasman suggested, and each time heard that clunk (this is very tricky as the valve knob is located where only a small child's hand could reach!), but the dripping from the overflow never quite stops. Is there anything I can do to prevent this myself, or is it a job for the pro?