Wiring problem perhaps??? help!

[darren popham]

Strange problem on a system as follows:

Ideal Classic NF40 boiler

room and tank stat seem ok and MV but (all with boiler stat on highest setting)

Call for HW only boiler flow is at 78degs (about right per spec)

Call for HW & CH or CH only boiler flow is always 50degs.

Result cold house and not very hot water and pump keeps going trying to heat the house with 50deg water!

any ideas

 

[sonray ltd]

whats the condition of the system water etc

 

[Deleted member 2053]

Try shutting down all but the nearest radiator to the boiler and see what effect that has. This sounds more like a faulty modulating solenoid on the gas valve, or the pcb, though I cannot immediately call this boiler to mind and am therefore not sure it even has a modulating gas valve!

 

[darren popham]

Water condition - bit murky but not to bad, system was powerflushed a year ago.

Will trying shutting down all but 1. What should happen flow temperature increase??? As I think it does increase when the house is warmer and all the individual TRV's shut down certain rads

I dont know if it has a modulating gas valve or not (!) but a spare gas valve looks about £90 or the PCB is about £100!

O could probably do the PCB myself but the Gas valve sounds very "corgi registered" to me! any morethoughts on the above?

 

[Deleted member 2053]

It does sound as it the problem is due to the boiler not running at full rate. This would be borne out by the flow temperature rising as you take radiators off line. Hence my notion that it might be a modulating valve. If so there is more probability that it is the valve solenoid than the PCB. Better get a CORGI man. Whereabouts in the country are you?

 

[darren popham]

Graham,

Many thanks for your help. Firstly I am in Bedford (a bit far from Devon I suggest - that would be one hell of a call out charge!)

A bit more progress last night! Effectively what is happening is that the boiler is cutting out before reaching flow rate temp (as if the thermostat is cutting in) and in my limited knowledge I see that it should work like say a kettle i.e keep going until temperature reached.

So last night and in the traditional way I would give the control box a small "wack" each time the boiler cut out and lo and behold it would come back on again!! Using this method I managed to get the flow temp up to about 75 degrees. A bit low compared to spec but 20 degrees higher than i was getting!! So I suggest that some electicrical connection (of sorts) in the control area is problem, any ideas.

Thanks to all that have tried to help!

 

[PipeStrangler]

Could be a dry joint on the circuit board. I had one develop on a Pottertom Puma combi which lead to a similar intermittent problem on the CH output.

I Identified the dry joint by prodding the PCB board with a neon test screwdriver, in dim light conditions, but being careful where I prodded. Sparks / crackling occurred and on inspection in good light I noticed some brown discolouring / staining on a soldered joint in the vacinity. Isolated power supply, re-soldered (electronics type with soldering iron, not blow torch), and hey presto : saved a ton plus on a new PCB, and problem solved.

Hope this helps... Rgds - Jon.

 

[darren popham]

Dear All!

Well checked again and using fault finding chart it says is neon light 12 on or not (12 is for boiler calling for heat) if not remove sensor (thermistor sensor) from the PCB board if neon light 12 lights then replace sensor.
So removed sensor and light (and boiler) came on so looks like Thermistor sensor. Couple of questions.

1. Does this seem to make sense or as I fear is this to simple?

2. Can a DIYer replace a thermistor sensor or is that a CORGI job???

Comments please

 

[Deleted member 2053]

Yes a thermistor fault does sound reasonable but doesn't quite fit the 'giving the boiler a whack' routine which suggests it may be the circuit board. However theremistors are cheap and circuit boards are not so try that first. It is not illegal to repair your own boiler as long as you are competent. It is up to you to decide whether or not you are competent for this task.

Potterton boilers are very prone to dry joints on the circuit board. Ideals, in my experience, are less prone.

 

[darren popham]

Thanks to all for the help on this.

At moment the boilers is fixed! All i have had to do is remove the thermistor on the PCB and put it back on and the boiler now works fine.

So it appears either dodgy connection at PCB end which taking on/off has cured or its intermittent and is currently working ok.

If need be I will order the thermistor sensor and replace.

Hope this is of help to future readers and thanks again to all comments