sludge in the tank (and in the system?)

[glider26]

Hi,

We've got an open system with a minimiser SE boiler. We moved into this house in May last year and the boiler kettled a lot so over the summer I added a sludge remover to the system, ran it a bit, drained it and filled it back up. It ran fairly quietly until recently. There's a bit of kettling now and a bit of whistling shortly after the burner lights up. This whistling def does not come from the fan as I've tested it separately.

When I came home today the boiler woudn't stay lit. The fan came on, the gas valve opened and the burner light came on for 1-2 seconds and then went out again before the gas valve closed. I had a look at the control board and the number 2 LED (lockout) comes on after the burner shuts down. I tried to light it several times to no avail. The CH and DHW both seemed to work. I went in the loft to have a look at the F&E tank. Suspecting that there wasn't enough pressure in the system I made sure that nothing was obstructing the output of the tank and I topped it up a bit by lowering the plunger. I noticed that that there was a lot of sludge in the tank (brown and black).

When I came back downstairs, I tried to light the boiler again and this time it worked. It's been working all evening with several light-ups as commanded by the thermostat.

I feel none the wiser as I have no idea what the problem was and suspect that it will come back. Any ideas? It has been very cold recently (-4), so perhaps that's got something to do with it? What about the sludge in the F&E tank, I didn't think that there was anything in there to corrode, so is it normal to have sludge there? Our water cistern which is next to it has (thankfully) no such cr*p in it.

Thanks for your help.

Glider26

 

[Hugh Jaleak]

Sludge is a product of electrolytic corrosion taking place inside your system. Combination of metals, (steel rads, copper pipe, brass valves and cast iron boiler) all react together with the water causing the sludge. System is basically rotting slowly from inside out.....

Chemical clean may help, if system is badly affected then powerflush may be needed. Either way you'll need to add some inhibitor when system is clean, the neutralises the water and stops the electrolytic corrosion.

F&E tank wants to be 1/3rd to 1/2 full, adjust ballcock if need be. The CH system when filled will use that same water until its drained off, F&E tank just 'tops up' as needed. The other tank will feed the hot water cylinder, so has a constant 'turnover' of fresh water through it, and should ideally have (at very least!) a tight fitting lid to stop any detritus getting in.

 

[glider26]

Thank you. 2 questions:

1. Having raised the pressure in the system slightly past night (see 1st post), there was a leak from the boiler this morning. I opened it, dried it up, let some water out to reduce the pressure and it no lOnger seems to be leaking. Which bit (weakest link?) normally leaks in a boiler?

2. Is it normal to have sludge in the f&e tank itself?

 

[45yearsagasman]

Which bit (weakest link?) normally leaks in a boiler?

With that model......where to start. Unless they are serviced regularly and properly the heat exchanger gets so blocked that the flue gasses are restricted.(the exchanger is almost impossible to clean properly)
The result is distortion of the burner and the ignition and sensing electrodes.
Seals in the flue are known to fail. The gas valve and burner had an issue and a retro kit is available. The PCB was upgraded so it made 5 attempts to light before locking out(that should tell you something) Altogether not one of Ideals finest. Get it checked out and don't spend too much money on it, as it must be 10+ years old.
Sludge in your tank may not be a sign of system problems, but clean it out and get your man to test system water quality.