Sludge in heat exchanger affecting temp sensor ??

[davidzzx99]

Hi Guys, hoping someone can help me here

A week ago, I heard gurgling sound up in loft found vent pipe overflowing hot water into header cistern - called plumber, he replaced faulty cylinder thermostat but that didn't fix problem - eventually traced problem (we think) to boiler - boiler thermostat set to 2, but it always "clicks" between 0 and MIN = way too low - temp sensor is working fine, it just isn't getting very hot (poked into hole near top of heat exchanger) - suspect sludge (or something) in heat exchanger is preventing heat transfer to heat sensor ?? It's a 20 year old Potterton Kingfisher II, never had a problem with it. Plumber drained some water out of radiator drain plug, water seemed ok.

Plumber talking about full system power flush at £600, or new boiler at £2000 !! Eek.

I called Potterton tech support, very helpful, they seemed to say flush out the heat exchanger, which makes sense - and they said it's ok to use strong chemicals cos it's made of cast iron.

Does this sound the right thing to do ?? Is that an "easy" job (compared with full system power flush) ?? Just don't want to spend £600 or £2000 if we can avoid it.

Thanks for any help with this !!

David

 

[Tibbot]

So no-ones checked simple stuff like if the cold feed is blocked. Do rads and hot water cylinder get hot cos' if so it can't be heat exchanger.

 

[davidzzx99]

So no-ones checked simple stuff like if the cold feed is blocked. Do rads and hot water cylinder get hot cos' if so it can't be heat exchanger.

Hi, thanks for your quick reply. I'm sorry, I don't know if he's checked cold feed blocked. All rads & HW cylinder certainly do get hot. I'm not thinking the heat exchanger is completely blocked, just silted up enough to prevent the temp sensor from getting hot. It just seems weird that the temp sensor is no more than slightly warm. The Potterton guy also said something about putting in heat conducting paste - pls excuse my ignorance, but would that be around the heat sensor in its hole ?? Doesnt it seem a reasonable conclusion that a heat sensor that's not getting hot, not triggering the boiler thermostat, and so letting the boiler run too hot, would cause the vent pipe to flush out ?? Thanks & best wishes !! David 07739-314261

 

[Tibbot]

Coat the sensing phial with the heat sink compound. Try testing it in jug of hot water.

 

[Agile]

I'm not thinking the heat exchanger is completely blocked, just silted up enough to prevent the temp sensor from getting hot. It just seems weird that the temp sensor is no more than slightly warm.

The thermostat is near to top of the boiler ( I hope ).

Sludge settles to the bottom.

Is the system return to the bottom of the heat exchanger, that is the cooler pipe.

I am wondering if the flow/return have been reversed or more likely the pump has beeen replaced to pump in the wrong direction?

Tony

 

[davidzzx99]

Coat the sensing phial with the heat sink compound. Try testing it in jug of hot water.

Thanks again for your quick reply, very helpful. Back to my original question Could it be sludging of heat exchanger tubes that's preventing heat sensor from getting hot enough to turn off boiler ?? Thanks !! David

 

[davidzzx99]

Hi Tony, thanks for your quick reply, very helpful

>The thermostat is near to top of the boiler ( I hope ).

Yes, it's in a long hoizontal hole (I guess like a Smartie tube) at the very upper part of the heat exchanger.

>Is the system return to the bottom of the heat exchanger, that is the cooler pipe. I am wondering if the flow/return have been reversed or more likely the pump has beeen replaced to pump in the wrong direction?

Well we've lived here almost 20 years & I certainly have no recollection of these modifications being made.

Thanks & best wishes !! David

 

[davidzzx99]

>Sludge settles to the bottom.

I suppose when I said sludge I was thinking limescale, we live in a hard water area.

Thanks & best wishes !! David

 

[bengasman]

...Plumber talking about full system power flush at £600, or new boiler at £2000 !! Eek.

One does not exclude the other. If your "plumber" suggests a new boiler without flushing the system, he is clearly a cowboy.

 

[davidzzx99]

...Plumber talking about full system power flush at £600, or new boiler at £2000 !! Eek.

One does not exclude the other. If your "plumber" suggests a new boiler without flushing the system, he is clearly a cowboy.

Thanks for your message - I believe the price of the new boiler would include power flushing the system before installing the new boiler - but I still need someone to confirm (or otherwise) that another option is simply to clean/flush/whatever the heat exchanger which surely would be more cost effective than cleaning the whole system. For example if there's a mark on my wall I can repaint the wall without repainting the whole house. Thanks again & best wishes !! David

 

[bengasman]

If the boiler itself works without any problems, I don't see why it should be replaced.

 

[davidzzx99]

If the boiler itself works without any problems, I don't see why it should be replaced.

Thanks for your kind reply. Engineer said if replace the heat exchanger, then that could cost £500 plus £500 labour, but what if something else goes wrong, so worth spending the extra to get complete new boiler. Thanks & best wishes !! David

 

[bengasman]

Same question essentially; why would you change the heatexchanger, is it leaking?

 

[davidzzx99]

Same question essentially; why would you change the heatexchanger, is it leaking?

Thanks for your quick reply. No, not leaking - but engineer is saying (I think) that if it's sludged up (not completely, as heating/water is working) or limescaled then need to power flush entire system, or rpleace boiler, which to me sounds excessive. Engineer's boss has requested to come & see for himself this afternoon, as it's taken several visits so far, and I'm just trying to get system fixed for my family as soon as poss, and it's not easy because of course I don't understand all the options & implications - sorry for being useless. Thanks & best wishes !! David

 

[bengasman]

No, not leaking - but engineer is saying (I think) that if it's sludged up (not completely, as heating/water is working) or limescaled then need to power flush entire system, or rpleace boiler, which to me sounds excessive.

Proper powerflush will do the job, absolutely no need to change the boiler by the sound of it.

The question I would ask myself: "If it takes me this long to come to a questionable solution, do I want this company to powerflush the system?"