Central heating woes

The history

Some of the radiators were taking ages to heat up and the boiler was cycling every couple of minutes so something's up.
Sludge?
I put in some desludger, waited a couple of days but nothing much had changed
Low flow?
Whipped out the pump and found this, a rather blocked impeller

so I went and bought a new one.

Ok so KTM doesn't make CH pumps and it really looks like this

Still no real improvement so I ran it for a bit and then did a thorough flush, or so I thought.

Ran the pump at full speed with no heat, one radiator at a time, drained from the bottom of the system with the header tank still connected. A few hours later

and this muck had been removed. Not a lot bearing in mind the age but I think that a lot of sludge has also been removed.

Here's a closeup of the magnetic stuff

Now all of the radiators get heat at the same time so the headers are flushed but it's still cycling too much with the boiler stat set low and the pump running full speed.

To be continued.

Boiler stat max

Pump speed max

35s on

60s off

Water outlet temp 56°C eventually

Time to check the thermostat and overheat switch

I then tested the cutoff temperature using 

a thermocouple and a mug of hot water:

• Boiler stat min, turned off over 68°C
• Boiler stat max, turned off over 87°C

No figures available but it seems about right as the overheat protector would trip at about 95°C.

You don't need a meter, the gas valve goes clunk.

Top tip: tie a bit of string around the phial circlip before removing it. The phial takes a bit of a pull as it was installed with thermal conductive paste. It'll go back with Copaslip.

Made a half arsed attempt at testing the overheat protector with a fag lighter, it got pretty hot but stayed open circuit; I presume this is normal otherwise the boiler wouldn't light.

It's still in bits and I'm going down the pub.

To be continued.

Burner pressure was over 4½" w.g. The manual says 4.2" max for 30,000 Btu/h. The calculated load was 29,000 so it was reset to 100mm.

Reassembling the phial and circlip was a pain with the limited access and lack of a third hand but it's in.

On test:

Pump speed 6 out of 7

Boiler stat  turn off temp

1                    44

2                    56

3                    64

4                    69  On for 1m 25s, off for 35s

5                    72

Pump speed  Boiler ∆T  °C

6                   20

5                   got bored

4                   20

3                   15

2                   24

1                   27

So that's telling me very little except that I'm not waiting long enough for it to stabilise between changes so I am going to set both at 3 and go down the pub

To be continued

Flush results TDS ppm

Tap water      400

Boiler water   660 - bugger, ideal is <1.1 *400=440 but like a berk I forget to take a sample of the water before the inhibitor was added so dunno what effect that had

ph 8.2

I seem to remember from the dim distant past that checking boiler and radiator ∆T is a laborious job best done when it's cold outside and the boiler is running at capacity so I'm going to settle on pump and boiler stat at 4 then see what's happening on Christmas day.

Old tech

New tech

It's a barby radio thermometer with two probes. Use a Terry clip to fix the probe to the pipe then clip over a short length of pipe insulation.

Flue gas temp is 130°C at an ambient of 17°C, boiler stat on 4. Typical range is 120-200ºC for a non-condensing boiler.

To be continued