Boiler woes

[Channel Hopper]

I've got an intermittent fault (again), on the house boiler.

Could be the pump or the circuit board (I think it's the board myself)

Have a gander at the following flow chart, there seems to be no point where the pump can be diagnosed as the problem.

 

[Lazarus]

Well you can further eliminate (or otherwise) the Pump by removing it, dismantling the impeller housing and manually freeing it off: Most apparent Pump failures are actually stalling caused by foreign bodies (swarf) and can be easily remedied. They rarely burn out.

The down side is that stalling is generally continuous rather than intermittent so I'm inclined to agree the cause lies elsewhere.

 

[MarkW]

Common cause of intermittent problems like this is a dry joint on the circuit board.Have a look at the soldering of the circuit board connector for the pump.You may have to use a magnifying glass,also check the pins and connector.If there are fine cracks it will need re-soldering. What exactly goes wrong?Normally when a pump stops there's an almighty noise when the boiler overheats.

 

[Vipersan]

If there are relays on the control board ..they are always suspect..
not o/c coils ...just arcing on the contacts causing pitting and occasional intermittancy.
A temporary fix can be had by opening the the relays (if faulty) and a light cleaning with emery paper.
But if confirmed faulty ..they really need replacement ..
min 240v 10amp if memory serves.
rgds
VS

 

[Channel Hopper]

Well you can further eliminate (or otherwise) the Pump by removing it, dismantling the impeller housing and manually freeing it off: Most apparent Pump failures are actually stalling caused by foreign bodies (swarf) and can be easily remedied. They rarely burn out.

The down side is that stalling is generally continuous rather than intermittent so I'm inclined to agree the cause lies elsewhere.

The system used to start straight away after the heating was put on, and a varying number of minutes after a demand for hot water. Nowadays though ity could be up to an hour before the boiler kicks in.
When it does start though the pump makes no out of the ordinary noises, and runs fine until the system is shut off. The flow chart shows a check for 240v across X3 (pump connections ?), and when there is no start, there is no voltage.

Will take the board out for a closer inspection tonight, though I ought to find where I left the solder first.

 

[MarkW]

So I assume the gas doesn't light either?I assume this is a combination boiler where all is included ie pump and there's no hot water tank?Normally on a combi before the gas is lit, and the pump started, the fan is started to expel exhaust fumes.To make sure this has happened there's a vacuum switch connected to near the fan,by a tube, so when the fan is on there's a vacuum and the switch goes short circuit,allowing the boiler to start.Check in this area,is the fan starting,is the switch going short circuit(voltage across goes to zero).Good luck

 

[Vipersan]

Just read Marks reply ..and it made me remember something..

...on mine there is also a fan near the flue (top of combustion chamber) which activates a switch via plastic tubes ..ie pressure driven.
This does go faulty ..but also blocks up..
I had this happen once and was advised on a plumbing thread to change the unit..
On my boiler referred to as the 'Venturi device'..
Well I dug a little deeper ..and found that this device rarely fails ...but simply blocks and is easily fixed....by disconnecting the 2 rubber tubes attached to it ..and blowing a good lungful of air as hard as possible through the unit ....pipe in mouth ...then reversing the procedure and blowing air in the opposite dirction through the other pipe..
Result ..after reconnecting the tubes the boiler kicked up and remained working ..
I did this over 4 years ago ..and have had other boiler issues since ..but NOT with the venturi.
Mebbe you have something similar on yours ?

The point being ..If the venturi/fan assembly cannot expel flue output...
The boiler refuses to start and /or can shut down.
Protection from fumes build up..
rgds
VS

 

[Channel Hopper]

Thanks, but the air pressure switch (and fan) are further down on the flow chart, which suggests these do not have a direct impact on the start up.

The flow chart could be at fault though, hence my original question

 

[Vipersan]

Thanks, but the air pressure switch (and fan) are further down on the flow chart, which suggests these do not have a direct impact on the start up.

The flow chart could be at fault though, hence my original question

Back to suspecting the control pcb I think..

 

[MarkW]

Fair enough but is the fan coming on when the fault on?

 

[2cvbloke]

google the make & model (I would have, but, there's none posted), probably someone out there with the same fault and a solution, or just call an engineer in, just incase it's serious...

 

[Vipersan]

google the make & model (I would have, but, there's none posted), probably someone out there with the same fault and a solution, or just call an engineer in, just incase it's serious...

I have a feeling CH want's to deal with this himself ..
I know I would ..
Not afraid to tackle any boiler problem ..but I draw the line ___sensibly___ when it comes to the gas.
Gas = Time to call a trained professional..

 

[Terryl]

My experience with heating boilers not starting or running as long as they should led to some problems with the "Over temp" switch being faulty, most systems (well the newer ones here Stateside do) have an over temp, low water or other safety cutoff switch, if one of these hummers goes bad or intermittent you can loose some hair looking for a fault in the controller board.

Look through the schematic (if you have one) and see if there is an over temp, over pressure or low water sensor/cutoff switch in the circuit somewhere, a simple check with a DVM can tell you if it is out to lunch, (careful as you may have to do this with the system powered down) a bypass clip or jumper can tell you if it is the problem or not, just be careful.

One system I looked at had an over temp switch that had tripped, found out that there was a very small hard to find reset button on it, pressed that and it worked fine, it tripped a few days later, replaced the switch and all was well.

As far as GAS goes, I use about 2 tea spoons of baking soda in a glass of water, works faster then the over the counter stuff.

 

[Channel Hopper]

Resoldered as many connections as I can see on the board, there are small IC's on the rear of the panel that are impossible to deal with though.

Double checked the thermistors in the demand piping and they check out. The manual states that if there is a 5V between the pins to the DHW switch when there is a damand then it's either the water regulator switch, wiring, or the board. I've checked the first two, though I cannot get to the mechanical regulator itself as it is behind a very awkward 24mm brass nut.

 

[Lazarus]

Would I be right in remembering you had a dicky Diverter valve not so long ago - or was that VS?

Not sure if or how that might be relevant, but presumably it reports its state to the Control Board?

 

[MarkW]

If you have a 2 or 3 port diverter valve then you don't have a combination boiler.This would be my first port of call(pun intended).They can get sluggish and take time to move and make the circuit that starts the boiler.You can take the actuator off and see how easy it is to manually turn the valve.Make a note how how the actuator comes off and the position of the valve, when you do this.Cheers

 

[Channel Hopper]

If you have a 2 or 3 port diverter valve then you don't have a combination boiler.This would be my first port of call(pun intended).They can get sluggish and take time to move and make the circuit that starts the boiler.You can take the actuator off and see how easy it is to manually turn the valve.Make a note how how the actuator comes off and the position of the valve, when you do this.Cheers

Diverter valve is not the problem, plunger working as it should when demand is there

 

[MarkW]

If you have a hot water tank the thermostat on that can give funny problems.Like all is well until the tank is up to temperature then the boiler stops for the heating.Found that the plastic cover was stressing the control knob and effecting the contacts.Keep going!You're wearing the bastard down.

 

[bim]

If it was a combi boiler (but I think this has been eliminated ) expansion pressure vessel low pressure in this can cause all sorts of problems ie over heating, causing thermal cut out etc. Also this can cause the pump to act irregular. From memory I think it should be 1.5 bar with a bike pump.

 

[Channel Hopper]

If it was a combi boiler (but I think this has been eliminated ) expansion pressure vessel low pressure in this can cause all sorts of problems ie over heating, causing thermal cut out etc. Also this can cause the pump to act irregular. From memory I think it should be 1.5 bar with a bike pump.

It is a Combi 82 (Wickes/|Halstead) and yes there has been an issue with a loss of pressure before now. I did pump up the expansion chamber a few weeks ago, but will look into trying it again. There has been no thermal cutout for a while.

The boiler did start up normally this morning, so I may have got rid of whatever breaks there were on the board, but I'm still convinced it needs replacing.

There is no hot water tank in the system, nor room thermostat.