Hot water venting into F&E tank

[Vee239]

Good evening, I’m hoping for some advice on the following problem at my parents house.

It is a 'normal' vented system . .
> Cold water storage tank on a platform in the loft
> F&E tank on the floor
> Vent pipes go over both tanks with a separate overflow for each tank
> Indirect hot water cylinder in the loft
> Boiler is an old wall mounted Potterton Neataheat 10/16 (at least 20 years old, probably older).
> Motorised valve is fitted but doesn’t look like it works. Putting the heating on water only does nothing.

My problem is that about a cupful of hot water ‘spurts’ into the F&E tank from the vent pipe causing it to overflow. This happens when the boiler is set medium-high and continues to do so every few minutes until the boiler is turned down. The room thermostat is not connected.
Is looks like it’s been overflowing for some time as the water in the tank is discoloured with a brownish tinge and the outside wall shows evidence of a long term leak.
I cannot work out if the vent pipe comes up from the boiler directly below it in the Kitchen or if is from the hot water cylinder.

Can someone help with my understanding . . .
Does an indirect HW cylinder have a vent or is this pipe likely to be coming up from the boiler ? (It is directly above the boiler 2 floors below)
If the coil was gone, would water come out of the pipe or is it likely that the boiler downstairs is getting too hot.

Ps : Tony (Agile) are you based around NW London ? If so I’m sure you’ve done some work at my own place a few years back. You kindly came out in the middle of the night (about 12.30am iirc).

Thanks in advance for any help/advice

 

[hi-spec plumbing heating]

>I cannot work out if the vent pipe comes up from the boiler directly below it in the Kitchen or if is from the hot water cylinder

if it got brown water and it's the f/e tank it will be the vent pipe from the boiler.

vent pipe from cylinder go's into the cws (large tank)

it sounds more like the system is sludged more than coil gone.
what speed is the pump set at ?
and boiler stat ?

 

[Vee239]

Pump was set at 1 (of 3). My dad put it to 2 yesterday.
Not sure about boiler stat, the room thermostat is not connected and the dial on the boiler goes from 1-6. This is what they iuse to control the heating. Anything over 3 seems to cause the venting.

Is it a diy job to get rid of the sludging or do I need to get the pros in ?

 

[hi-spec plumbing heating]

clean the f/e tank out, use a fernox or sentinel sluge cleaning chemical.
have a look a their sites.
diy job but if sludged to bad and chemical don't shift it you may need it powerflushed.

 

[Vee239]

OK thanks very much for your responses, will have a go at putting the chemical through it.

Out of interest, why does the venting stop when the boiler is turned down ?

 

[hi-spec plumbing heating]

your not allowing it to heat the water to a high temp giving the pump time to pump round system.

 

[Vee239]

Right, will be putting fernox through it this w/e before the weather really turns.
Does the boiler also have a stat ?
I'd like to check if it is working but could do with some advice as to what to look for.
If I'm being silly and its a job best left to the pros feel free to say so & I'll get someone in.

 

[JohnD]

a chemical clean is an easy DIY job

Make sure you use the cleaner not the inhibitor!

It will be better if you have plenty of drain-offs (especially if you have any radiators fed by drop-down loop from above, in this case you need a drain on each radiator but you can buy radiator valves with drain-off for a few pounds, and this is an ideal time to fit them

If the system is very dirty leave the cleaner in for a week or more (see the instructions)

If you can afford a Magnaclean device as well, for about £100, it will be a tremendous help in capturing the loosened sediment, and will carry on working indefinitely, even after you've finished the chemical clean, flushed, and refilled with inhibitor. It is fairly easy to fit if you are draining anyway. It just needs two pipe cuts and to do up some compression joints with your big spanners. You will be surprised and delighted to see how much sediment it collects even after you think the system is clean.