DIY Central Heating Flush

[Peter]

How practical is this as a DIY job and how can it be done?

The cost of a power flush is silly money.

[John Rumm]

Its easy enough to do. There are several approaches. BS 7593 gives chapter and verse.

What sort of system have you got at the moment; vented or sealed?

Sealed systems are quite easy to do, basically open a drain point, turn on the filling loop full flow, then go round and turn off all rads but one. Let that enjoy full flow for a few mins, then open the next rad and shut off the first. Keep going until all done.

If you want to be extra anal, then take off each rad in turn, take it outside and flush it through with a hose.

Before you start add some system cleaner and get that circulating for a few hours at a minimum (or if ripping out the original boiler etc, then it can circulate for a couple of weeks)

[charles]

the firm who came here removed the pump and ran hoses to their own pump and filter. All radiators were closed and then each one opened in turn and effectively the water circulated through that one radiator. All sludge was trapped in ther filter. Once it ran clean, the work moved on to the next radiator. About 7 hours work in total.

[geoff]

In message , Peter writes

Well, if a central heating fitter can do it ...

are you trying to descale or desludge?

[A.Lee]

Indeed!

Can I pick your brains please Geoff? Baxi FS801 floor standing gas boiler 30 ish years old.

Starts up fine, runs for 3 minutes or so (HW (gravity only) or CH (pumped)), you can hear the water hissing (getting hot), then the RCD trips. I had a quick look at it, and there is very little electrickery in there. I pulled out the thermostat to see if it was that causing it, but it still tripped once the water got hot with the Thermostat pulled out (it is a 'cigar' stat, pushed into the front body)

Do you know what could be causing it?

Oh, BG have been round, - cannot be repaired, no spares available now. A google this morning shows everything is available at reasonable prices still.

Thanks Alan.

[charles]

not Geoff, but I wonder if the pump is at fault?

[A.Lee]

No, as it happens with the HW on - no pump involved. The CH runs for 2 or 3 minutes, as does the HW, then trips. If it was the pump, it would be likely to trip immediately, or not at all if the HW only is called.

[charles]

but the pump is physically still there in contact with the water even if it's not being asked to run. A neutral/earth short could trip an RCD. It might need a bit of heat to bring on the fault.

[A.Lee]

Yes, after a phone call from Adam, even though the pump is not turning, there could still be a neutral - earth fault occuring, so I'll go back and disconnent the pump completely to see if that sorts it. Thanks Alan.

[ARWadsworth]

And if that fails then Geoff is the man with the knowledge.

Charles has suggested the same thing as I did in our phone call. I have seen it happen before.

[A.Lee]

Still tripping with the pump disconnected. I'm looking at the thermostat as the likely cause, the only other electric fitting is the gas valve, and presumably that is just a on/off switch inside it? The thermostat is the cheaper one to replace too.

[geoff]

These predate the boilers I know but

if it cuts out after a couple of minutes, then the thermostat has to be the next port of call after the pump, these were pretty generic in those days. The gas valve has a solenoid which lets the gas through - its a coil with a resistance of a few thousand ohms, nothing much to be time or temp dependent

[NT]

Could be any part that mains leccy reaches. There's not much mileage in guessing - get yourself a multimeter, check L&N to E resistance for each mains part, after temporarily disconnecting it, and odds are you'll find where the problem is

NT

[geoff]

You missed the bit "Starts up fine, runs for 3 minutes or so"

Odds are ... you won't

[ARWadsworth]

I can assure you that Alan has a rather smart looking 17th edition tester:-)

[Andrew Gabriel]

Does it trip when the stat clicks off? Try turning the stat down before the 3 mins and see it that trips it (or the opposite - turn the stat up and see if that delays the tripping).

[A.Lee]

And, after changing the gas valve today, it was traced to a manky burnt piece of wire that connected the gas valve. Once the wire was replaced, all was fine. The gas valve was corroded, so was changed anyway, and we saw the BG 'service', 6 months ago. The flue chamber was covered with dust, the burners filthy with rust too. The flue cover was the wrong way round, with one screw corroded into place. It had been off before, but a long time ago, so the BG chap had never taken it off while doing his 'service'. The customer cancelled his contract with them while we were there.

Alan.