Scale Problem? Potterton Boiler

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Hi gents, seems there is a lot of knowledge on this site so thought I'd try picking your brains.

We have had seemingly erratic HW and CH when required by tank/ room thermostats from our gas fired Potterton boiler for about a year. This is a pressurised system and the boiler is about 9 years old, was put in by a building contractor when the house was extended and extra rads added, etc. Originally suspected the zone valve, head has been replaced (last winter) and problems seemed to reduce for a while, but now it seems that the boiler will only fire for a short time and then the water supply from the boiler to the DHW/ CH goes cool. (It takes a bit longer to happen if only CH on but happens with any combination of DHW and/ or CH.)
Replaced a non functioning rad during the summer, it had sludge in it, did a partial flush of the system then (just from the fill to the open connection where the rad was removed) and got some black stuff out, considering a power-flush but wondering if the problem could be scale and hence this would be ineffective/ waste of money?
We live in a hard water area, the system appears to have been treated when new for corrosion but maybe not scale.
Coud this be a scale build up problem? (Has it been long enough?)
How can it be treated?
Is it worth doing a power flush (or maybe a mains water flush which I could probably manage myself?)
 
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Professional power flushing is expensive and often not done very well either.

If you can properly mains flush your whole system that will be better as it will not cost you anything.

Afterwards add X400 for 4-6 weeks and then drain and add X100.

Its unlikely to be limescale unless the system has been wrongly operated.

Tony
 
Certainly worth doing that, but sludge tends not to affect HW so much.
You may have a faulty thermostat in the boiler, or it's possible if your water is really hard, that the cylinder is full of limescale.
Do you have an electric immersion heater - if so does that work?

WHile the HW is heating, does the flow pipe from the boiler stay hot?
What boler is it, by the way?
 
Hi gents,

Thanks for the quick responses. The boiler is a Potterton Profile- can't see any model no, etc.

There is also an electric immersion element in the cylinder and it seems to work, at least it provides much more hot water than than boiler ever does. It hasn't been used much until this year, but that's how we get most of our hot water now- does the scale build up on the outside of the heating element(s) (i.e. in the hot water tank) over time- could it therefore have knackered the boiler exchanger first and now be working on the electric immersion element? (However this would not explain the CH problem, would it?)

Any further input appreciated, happy to do any simple trial and error on this.

Will try the mains flush today, found the process in the wiki, just got to check if I have operable valves in the right places!
 
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WHile the HW is heating, does the flow pipe from the boiler stay hot?

Is the temperature knob on the boiler turned right up. YOu may need pliers to turn it, because the knobs always break.

It's sounding likely that the boiler thermostat is faulty, turning it off too soon.
 
Sorry ChrisR, missed that.
The supply from the boiler stays hot for a short time (sometimes an hour or so, but often only minutes) and then stops- I guess the boiler thermostat trips and stops it heating the closed loop. The pump stays running and progressively cooler water continues to be circulated, as the tank and/ or room thermostats are still calling for heat. (They both seem to stop and start the pump and open/ close the zone valves properly, btw.)
The boiler thermostat is set at max since yesterday as I figured this could be part of the problem- it now seems to run a little longer before it "trips" but the symptoms are the same.
 
If they pipes is cold and the pump's on and the flame isn't, you need a new thermostat. Corgi job - unless you know how to test...
 
The thermostat on your model should not normally be operated above 3½ otherwise the margin between operating and overheat stat becomes too small.

Its important that the pump is controlled by the boiler and a bypass is provided if the system can be totally closed off.

Tony
 
Thanks again Gents.

Spent most of yesterday working on the mains flush which of course hasn't made any difference, but at least I feel like I was working on the problem :) Good housekeeping anyway!

[The thermostat on your model should not normally be operated above 3½ otherwise the margin between operating and overheat stat becomes too small. ]

This could be vitally important bit of info! Have reset the boiler stat to 3 and it is firing now, will see how it goes and report. I'm sure it was already set to 4 or 5 before I pushed it up to max.

Otherwise I guess I will have to resort to getting a Corgi professional to test the boiler stats and replace if reqd- I am a Chartered Chemical Engineer so I can understand pressure, flow and a bit of water chemistry. etc., but I can also work out when not to mess with something I don't fully understand :)
My next concern will be how do I find someone to do this that won't rip me off- particularly bearing in mind it will probably be only the missus home when he has to call? Any ideas what it should cost?[/quote]
 
Just thought I'd provide feedback to close this out.
Got an engineer to come out from Heateam (the Potterton site directs you to them). Fixed fee of 236 quid for parts and labour. He didn't seem convinced it was the boiler control thermostat (he kept going on about sludge build up but that would surely cause an overheat trip) but did eventually replace it, along with a control circuit board that he said was a common failure problem.
Anyway it's working now, missus pleased and house is toasty. Water gets hot but still only a limited volume so I guess we still seem to have a hot water tank full of scale but will post separately on that if necessary.

Thanks for the help guys.
 
he kept going on about sludge build up

you sound like you don't believe him :confused:

put some Sentinel X400 sludge-loosener in, and see what it finds. 50p says the water goes deep black as it loosens whatever is in there.

if so, run it for a week or two before draining and flushing, and refilling with inhibitor.

(or did you do that before your previous flush?)
 
Hi JohnD,
I did add X400 after the last flush and I'm planning on leaving it in for at least 4 weeks as suggested in other posts, will flush it out again mid Dec., and will let you know the results. :) I expect it will shift some sludge from the system, there are two original rads which never seem to give out quite enough heat even after lots of balancing effort which I hope will get cleaned out but I'm not so sure that sludge build up in the boiler is a problem.


At any rate the system is running now so there was definately a problem with the boiler control which seems to have been fixed, but it appears all the Heateam guy replaced was the circuit board- Potterton part no 407677. I kind of expected the boiler control thermostat to be a separate part but I guess it must be on the board, is that correct? :?:
 

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