Worcester combi boiler 28i junior

[mileso101]

Its and LPG system that has been serviced every year Its been so warm this year we have only been using it for showering and HW.

My partner said she ran the HW, it started to only work for 30 seconds then went cold, so she stop running it and after running it again it went really hot and goes cold again. this happened while I was working away so there wasn't much I could do .I found the pressure was basically zero on my return, so I refilled to 1.5 bar via the loop and tried again but had the same from all the taps and the shower.

I hadn't used the heating all year so tried that and apart from the pressure rising to 3 ( I blead the nearest radiator till it went back to 1.5) the central heating was fine for 3 hours till I switch it off manually ( its an old small stone house so the house holds the heat incredible well), though the pressure did fall below 1 again
there are no leaks that I can find from the CH system and the condensate pipe isn't showing any water.
I'm thinking it may be expansion vessel lost pressure.

Regarding the HW only could it be some sort of air lock ?. We had the water off from the water board while I was away, while they were digging up the road so stopped all the water for the street and I know when they left, my partner said the hot and cold water spurted from the kitchen and bathroom taps for a while

There are no errors showing on the boiler, when I run any HW tap, the burner comes on for about 30 seconds and then goes off.




thanks for any replies

 

[ianmcd]

your expasion vessel requires re-charging

 

[mileso101]

Thanks for that i thought it might be that the expansion vessel, though I've no idea how it affects the hw

 

[kidgreen61]

I'll bet a virtual £ that your plate HEX is blocked/gummed up with muck

 

[mileso101]

I'll bet a virtual £ that your plate HEX is blocked/gummed up with muck

Its a relatively new system, that's been serviced every year, I looked at the manual and its states over temperature shut down which then shuts off the gas valve which seems to be what's happening, ill pressurise the expansion vessel to 1 bar and see how we go from there.

 

[terryplumb]

Your expansion vessel pressure has no bearing on the domestic hot water running hot/cold/ hot/ cold repeatedly ,is that what all taps are doing ?

 

[mileso101]

Your expansion vessel pressure has no bearing on the domestic hot water running hot/cold/ hot/ cold repeatedly ,is that what all taps are doing ?

Yes every tap, when you run the HW. It runs cold as normal then gets very hot quickly and the the burner light goes off and the water goes cold

 

[martygturner]

Heat exchanger blocked...as per normal after the summer switch off/

 

[CBW]

Heat exchanger blocked...as per normal after the summer switch off/

????? Never heard of that before

 

[martygturner]

????? Never heard of that before

The amount of times on this forum alone when october/november comes around and its my tap keeps going hot and cold and you haven't noticed....are you deaf or something.

 

[CBW]

The amount of times on this forum alone when october/november comes around and its my tap keeps going hot and cold and you haven't noticed....are you deaf or something.

No not deaf, just seems a bit of nonsense. Also how can I be deaf for reading what people put on here? I would have to be blind.

 

[martygturner]

????? Never heard of that before

Also how can I be deaf for reading what people put on here? I would have to be blind.

Hmmmmmmm.....Just look below on similar threads...heating goes on and swoosh all the muck that has settled out hits the heat exchanger..see bunged up TRV, see why is my rad not getting hot...

 

[kidgreen61]

Why on earth would a system suddenl start corroding itself in the summer, just because it's not being used????

 

[martygturner]

Why on earth would a system suddenly start corroding itself in the summer, just because it's not being used????

Really....have you done any chemistry ?" the don't start suddenly corroding" pah !!! yes they do the moment you turn off the flow..

An inhibitor works by coating a rad, it does not stop oxidation in merely slows it. To work an inhibitor needs a minimum flow rate to keep coating the inside of a rad, during the summer pause the inhibitor will slip down the rad, its a mixture not a solution, ie it is not chemically bonded to water because if it was it would not be able to do its job. Basically as agitation ends the inhibitor falls out of suspension as it is only mixed with water. And therefore the top of the rad is left all defenseless, Inhibitors put oxides that have formed into suspension not solution ie they clump them together...that's how magnetic cleaners work, hence all that black sludge when you drain a system.

A cleaner on the other hand does put oxides into solution, ie they chemical bond with the water as cleaners are acidic and have a covalent bond.

In terms of sediment build up , oxides flocculate, that is they clump together in the presence of each other in still water, once they have formed lumps and have rained down to the bottom of the rad as black sludge hey presto you turn on the pump and round they go, ending up at the heat exchanger or sticking the TRV .

So in short an inhibitor inhibits, it does not remove or chemically alter the oxides that have formed, it just puts them in to suspension, its job its to stop corrosion, to prevent it. And when something is in suspension it can and will settle out if it is not agitated.

Oh and by the way water has around 20% by weight dissolved oxygen in it that is free to make oxides, so any bare metal will start oxidizing, so as the inhibitor slowly settles out of the water column....

 

[JonathanM]

An inhibitor works by coating a rad, it does not stop oxidation in merely slows it

All really interesting, thanks. This is probably going to sound really stupid, but why is the sludge black? I thought it would be rusty red.