Boiler woes

New seal / clips in, relief valve on pressure chamber OK but replaced anyway, and inflated to 1.3 atmospheres.

Everything running OK currently.
 
Issues again.

Central heating has been perfect all along, but in the past few weeks the hot water has been getting more intermittent, with the overheat cutting in more frequently (requiring resetting).

Having looked through the manual the diverter system pushes cold (and the new hot water) through the heat exchanger - not absolutely sure why - and onto the taps. However after a few seconds of the burner the pressure drops and the relief valve operates (again sometimes with the overheat).

I thought the diverter diaphram may have given up the ghost after a few years of constant use and possibly the relief valve may be cutting in too soon, so both replaced tonight with no improvement.

The pressure gauge does give some indication there is an excess of pressure before the boiler cuts out, and the gauge suggests repressurising when this happens, but I did check the expansion tank last time, and there was nothing wrong.

So, is the fault with the heat exchanger ? or something else I have not worked out as yet ?
(there's also a 'bypass' circuit mentioned, but I have no clue as to what it might affect, and appears only to be part of the central heating side of things.Boiler flow chart.webp )

Diagram below for clarity.
 
It could be that the heat exchanger is calcified or rusted up, this could/would cause a higher then normal system pressure.

One way to test this is to put gauges on the inputs and outputs of the heat exchanger, if everything is normal through it then they should read the same, if the output pressure is lower then the input, then the heat exchanger is blocked up.

Have ever had your water tested for hardness? Or excessive minerals?

If the heat exchanger is blocked up and you can remove it, a good soak in vinegar or CLR* can clear it up, you may have to use a small fountain pump to push the solution through the exchanger.

In your travels through the system did you see any signs of scale or calcification?

I know some around here have problems with too much iron in the water, so about once a year they have the system cleaned.

How this is done is the input water supply is bypassed, and the input run to a tank, then pumped through the system back to the tank, a solution of CLR is used to remove the rust and scale, the system is flushed out thoroughly before reconnection if used for domestic hot water.


*CLR an off the shelf Calcium, Lime and Rust remover.
 
If in doubt, call a qualified boiler tech, half the time they actually know what they're doing... :)

(I feel like I've said that before!!)
 
Terryl said:
It could be that the heat exchanger is calcified or rusted up, this could/would cause a higher then normal system pressure.
.....snip.....
One way to test this is to put gauges on the inputs and outputs of the heat exchanger, if everything is normal through it then they should read the same, if the output pressure is lower then the input, then the heat exchanger is blocked up.
.
Click to expand...

Thanks, no gauges here, and the heat exchanger looks like a real sod to take out of the system, letalone replace since it is really close to the base of the heater and has no identifiable way of removing it
 
2cvbloke said:
If in doubt, call a qualified boiler tech, half the time they actually know what they're doing... :)

(I feel like I've said that before!!)
Click to expand...

You did and no, last time cost me nearly three grand after condemning the whole heating/cooking/water system in the property (next door) when the fault was down to a gas pipe the same company had fitted two years previously.
 
Channel Hopper said:
Issues again.

Central heating has been perfect all along, but in the past few weeks the hot water has been getting more intermittent, with the overheat cutting in more frequently (requiring resetting).

Having looked through the manual the diverter system pushes cold (and the new hot water) through the heat exchanger - not absolutely sure why - and onto the taps. However after a few seconds of the burner the pressure drops and the relief valve operates (again sometimes with the overheat).

I thought the diverter diaphram may have given up the ghost after a few years of constant use and possibly the relief valve may be cutting in too soon, so both replaced tonight with no improvement.

The pressure gauge does give some indication there is an excess of pressure before the boiler cuts out, and the gauge suggests repressurising when this happens, but I did check the expansion tank last time, and there was nothing wrong.

So, is the fault with the heat exchanger ? or something else I have not worked out as yet ?
(there's also a 'bypass' circuit mentioned, but I have no clue as to what it might affect, and appears only to be part of the central heating side of things.View attachment 77379 )

Diagram below for clarity.
Click to expand...
I changed a heat exchanger on my boiler sometime ago.Going from your diagram,and my old one,the fresh cold water comes in at the rear left port and goes out hot from the rear right port and onto the taps.The hot water,from the burner, is pumped in on the front right port and out from the front left port and back to the burner via the diverter.These two circuits are completely separate.Hopefully this clears up the confusion in this area.ie the cold water in isn't connected to the output from the front left port.
Not sure what could be causing your problem but if there was a restriction in the heat exchanger,as Terryl suggests,then the heat from the hot water(from the burner)wouldn't be dissipated quickly enough (through the heat exchanger)and it would overheat causing the pressure to go too high as well.If the diverter wasn't moving all the way to the hot water position then perhaps it would keep heating the radiators and wouldn't cause the temperature sat to trip....I think.My money's on the heat exchanger.The new one I got cost about £50.Good luck.cheers
 
Thanks for that, I am surprised the pipes on the heat exchanger come in from the top as well, meaning any crap settles into the transfer system with no easy way out.

It's still going to be a sod to replace/clean it.
 
Channel Hopper said:
Thanks, no gauges here, and the heat exchanger looks like a real sod to take out of the system, letalone replace since it is really close to the base of the heater and has no identifiable way of removing it
Click to expand...
I take it there's no removable panel on the base for heat exchanger removal,there was on mine.
 
There might be but I'm seeing it from the top and I cannot locate a way of removing it from the other items in the boiler, unless it just needs prising with something of leverage (after I get a replacement of course).
 
Mine was held in place by 2 nuts that held lugs,attached to the heat exchanger,in place.The 4 water connections were push fit suckers that were fixed in place.So the nuts were removed and the exchanger was simply pulled away.I think it was made this simple because its expected to be changed because of water impurities.Good luck
 
Channel Hopper said:
You did and no, last time cost me nearly three grand after condemning the whole heating/cooking/water system in the property (next door) when the fault was down to a gas pipe the same company had fitted two years previously.
Click to expand...

Easy solution, don't call that company again, call someone else who is independent and accredited, independent techs (not the cowboys, of course) always want their customers to be happy otherwise they don't get any work... :)
 
MarkW said:
Mine was held in place by 2 nuts that held lugs,attached to the heat exchanger,in place.The 4 water connections were push fit suckers that were fixed in place.So the nuts were removed and the exchanger was simply pulled away.I think it was made this simple because its expected to be changed because of water impurities.Good luck
Click to expand...

Will check later (a bit more than later - I might open a bottle with the fish).
 

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You are right, the exchanger is held by two 'allen' bolts, so I might take a chance later tonight.
 
Make sure you turn the water supply to the boiler off else you'll get a surprise :eek: .Plus the mains.You've probably figured that though.And some water will leak out.When you get the unit out you could try reverse flushing it with a hose.You should be able to easily blow through the unit.When I put mine back I cleaned the 4 rubber connectors and put some silicon grease on them.
 
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The boiler has - apparently - been behaving itself tonight before I got home so it may have read this thread.

If I get some time tomorrow morning (when the family is out) I'll have a good look at removing and cleaning.
 
Done.

The inlet to the exchange (from the burner) was more or less completely clogged up, not with calcium, but rust and other debris, most likely from the radiators.

Flushed out the exchanger (including banging the edges) whilst full of soapy water numerous times until the fluids were virtually clear. reassembled and primed.

The whole system sounds a lot quieter as well but I'll keep an eye out for any leaks/noises over the next few days.
 

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I guess the next job is unblocking the sink... :-rofl2
 
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