Noisy 28 Cdi

[PEDANTICVINDICTIVEMAN]

Fitted my neighbour a 28Cdi 3 years ago, used cleanser and inhibitor at the time.

Problems are when on hot water it sounds like it is overheating, chug chug chug and nearly banging, (OH stat isn't cutting in though) when on CH it gets noisy when getting near cut off temp as well.
Gas rate is correct and according to flame and manometer seems to modulate on both HW & CH, had DHW exchanger out flushed through and not blocked or really very dirty, hot water temp to taps is ok, had pump out and cleaned, shaft ok, downstairs rads get hot so pump working ok, bathroom rad and byepass open.
Ohms reading on both sensors approx 2 ohms when hot, supposed to be between 1 and 30 so taking this to be ok as wouldn't suppose "both" sensors would be duff.
Thinking of taking off the gas to water HE off to flush out, anybody got any ideas on best way of cleaning and what with or any other ideas whats wrong with the beast.

 

[Agile]

I would do it in situ with the heating circuit isolated!

Tony Glazier

 

[ChrisR]

I got caught recently with a grundfos which was spinning, hard to stop, clean, and not very old. But it was going slow. It wouldn't take long to try a new head just in case...

(somewhere I've got a rev counter - something else to lug about in future!)

 

[PEDANTICVINDICTIVEMAN]

How do "you" clean the HE in situ with the heating isolated.

Yesterday I turned off the isolation valves under the boiler, then drained it via its built in drain points, this drained the feed tank in the loft as well , I then poked a peice of 15mm plastic down the 22mm feed pipe, poured X200 directly into the pipe, this put the X200 straight into the boiler, then turned the water back on to fully fill the boiler and tank, then ran the boiler for 10 minutes on hot water only before opeing up the isolation valves, hasnt made any difference.

How do you do it and what do chemicaldo you use ? Mr Agile

 

[ChrisR]

He'll tell you how he does it where there ISN'T a feed tank if you ask nicely, without using one of those Kamco pump adaptor plate thingies!

Do you know where you can get dhwhe's v cheap for cdi's? If not I'll tell you off air.

 

[Agile]

I cannot guess where the open feed tank was connected to the boiler. And 10 minutes is not long enough to have any significant effect. We allow 2-3 HOURS with 3-4 dosings for this job!

X200 is a mild non acid descaler for mildly scaled problems. Its so mild it can be left in the system.

I am very reluctant to suggest acid treatments if you are not accustomed to them, safety in handling, protective equipment etc. Also you can dissolve holes in the heat exchanger and pipework. DIY people read this are are encouraged to copy without the knowhow.

As I said before, this is NOT a DIY activity but if its limescale ( with real calcium lime! ) then sulphonic acid ( DS3 ) heated to about 80-90*C. If its iron oxides then citric acid ( DS40 ) heated to about 70*C.

Yet again, like brain surgery, this is NOT for DIY, you only get two eyes and they are not replaceable. I am surprised this site allows professional techniques like changing gas valves to be posted when they are not suitable for DIY.

Yesterday I went to an FMB mini seminar on Part P from a senior Building Control officer. It was interesting some of the DIY accidents and fatalities he mentioned.

Tony Glazier

 

[wedge69]

Perhaps this is not the most appropriate foruim, but out of morbid curiosity, do tell of these accidents...

 

[ChrisR]

sulphonic acid ( DS3 )

Sulphamic I think. Makes soluble sulphonates. As though anyone GAVE a damn.

 

[Agile]

""Sulphamic acid I think. Makes soluble sulphonates""

What crass stupidity of Chemists to call an acid that makes sulphonates anything other than Sulphonic acid! You are right though! No wonder (al)chemists were regarded as the closest thing to witches in medieval times and probably burnt at the stake.

R4 this morning had a pyrotechnic expert who said that in the 1700s if they burnt the kings palace by accident they got a sword through the heart.

I cannot give details of the accidents, firstly its not connected with descaling heat exchangers, secondly I cannot remember them because I was more intreagued by the response of the lady at the front from the FMB who curled up in horror at every example. One coming back was having your clothes burnt into the skin by HV shocks but that was not in domestic Part P.

Tony Glazier

 

[PEDANTICVINDICTIVEMAN]

Changed the sensors on HW v& CH, still makes a racket, Spoke to worcester today and apparently I have done everything plus more than they can come up with, final thing to check was pump over 150 ohms across L&N terminals, if lower to change the pump, well I got readings of 00.2@ 200k setting 0.19 @20k setting and .188 @2k setting, so they said change pump even though the pump is working on all 3 settings and heats the downstairs radiators, so going to change the pump head on friday, I think the head from a grunfoss 15/60 fits, can anybody verify this, clutching straws now as everything else checks out, cant see it being dirt as I fitted this boiler myself and all done correct and water clean coming from rad drain point downstais.

 

[Agile]

""final thing to check was pump over 150 ohms across L&N terminals, if lower to change the pump, well I got readings of 00.2@ 200k setting 0.19 @20k setting and .188 @2k setting""

That should mean that the pump is over 150 ohms and not needed to change. However it would give peace of mind to change it.

Probably you have done this already but have you checked the setup of the gas valve, min and max settings? Is this the stupid gas valve than needs a 2 mm and a 3 mm allen key to adjust?

Tony Glazier

 

[PEDANTICVINDICTIVEMAN]

Yep, gas settings check out ok using the min/max and normal positions on the back of the pcb, gas rates correct and operate as they should and modulate as you turn the tap down on normal position.

Confused on this ohms caper, worcester tech say should be over 150.00 ohms, readings I am getting are all point something, not something point no matter what position the the multimeter is set at, am I missing something on this ohms business ?

 

[Agile]

Yes! You are missing how to read your meter.

Really a simple auto ranging unit would help you with less effort.

A "K" is a thousand ohms.

1 "K" is 1000

so 0.2 "K" is 200

Your readings are what Worcester wanted you to find. However since there seems to be a flow or blockage problem then changing the pump would be advantageous to eliminate it or find the problem. Have you inspected the impeller? Debris there will reduce the efficiency.

Also merely measuring resistance will not confirm the pump is working correctly. There is a capacitor of about 2 uF ( Microfarad ) and that has to be correct otherwise the pump will not spin fast enough.

By replacing capacitors, I have successfully repaired some of the long reach pumps used on some of the combis as these are not available any more.

A blockage could be a bit of plastic, or metal not just scaling or debris. Or it could be the pump not turning fast enough. Without Chris's tachometer that can be difficult to confirm. I wonder how it works?

Your repeated pleas that you have properly treated the water should point you to the pump. Correcting by changing the pump will be the jury!!!

Tony Glazier

 

[PEDANTICVINDICTIVEMAN]

Cheers mate for the info, yea had the pump and DHW exchanger out twice now and clean as a whistle, thanks.

 

[Agile]

You have had the DHW HE out but since the problem is common to HW and Ch then I would suspect a common item, either the main HE or the pump or even the pipework or diverter!

Tony Glazier