Halstead Finest Gold: boiler not firing on hot water demand

[andrewedmondson]

My Halstead Finest Gold has no hot water.

Turning on the hot water tap does not fire up the boiler.

If the CH is on, turning on the hot water tap turns off the burner.

The microswitch is being activated by the diaphragm. There's around 5V across the microswitch.

Last year I cleaned out the heat exchanger because the HW was cycling hot and cold.

A new thermistor was needed a few years ago for a different problem.

I've run out of things to check. Any ideas?

Thanks

 

[diamondgas]

Check for sticking pump flow switch, the one on the top! I think it's this model that checks that the pump stops before starting it back up again and setting the ignition sequence into action.

 

[andrewedmondson]

Thanks for the help.

This primary flow switch seems to be working OK. After switching on the power, a pin activates the switch. After a few seconds, the pin retreats and the switch clicks off.

 

[diamondgas]

If it's not the flow switch then check the APS. I am right in thinking that this model Halstead turns everything off before firing back up once more when you turn the hot tap on whilst the heating is on?

 

[andrewedmondson]

Could this be faulty, given that the central heating side works OK?

I'll have a look at it.

 

[andrewedmondson]

On powering up, the air switch clicks on. It clicks off after 15 seconds.

 

[diamondgas]

Could this be faulty, given that the central heating side works OK?

I'll have a look at it.

Andrew, if I'm right then what I've had before is the primary flow switch spindle sticking/ not retracting far enough. The PCB doesn't recognise that the flow has stopped so doesn't re-start the ignition sequence turning, in effect, everything off! I'm not sure of the model boiler I've seen this happen on but I know it occurs! Equally it may well check the APS in the same way!

 

[diamondgas]

On powering up, the air switch clicks on. It clicks off after 15 seconds.

What happens to the switches etc. when the boiler is running merely in central heating then you turn a hot tap on?

 

[andrewedmondson]

Interesting.

The CH works fine.

When it is on and I turn on the HW, the burner goes off immediately.

1 minute later, with the HW tap still open, the burner fires up for 4 seconds then dies. This happens just after the primary switch turns on. This repeats every minute.

I don't think the air switch moves, but I am having to leave the boiler to turn on the water.

 

[diamondgas]

Hi Andrew, you've probably got the thing sorted by now! I'd be interested in knowing what the outcome was?

What you're describing sounds like a switch being recognised then dropping out then recognised by the PCB again! I'd be checking resistances through the micro-switches. Sometimes they make but have dirty contacts that the PCB will recognise sometimes and not other times!

 

[andrewedmondson]

Hi

No luck yet. Thinking of buying a refurbished PCB for around £60.

But I'll have a look at bypassing the micro switches and seeing if that works. I put a screwdriver across the contacts of the DHW switch but I'll try joining the wires instead.

I'll let you know how I get on.

Thanks for the interest.

Looking forward to a nice hot bath.

 

[andrewedmondson]

You were right ... it is the micro switch for the DHW!

I joined the wires directly and the boiler fired up.

What is weird though is that I tested the switch using my meter and it showed 0 resistance when closed. That was also one of the first things I tried.

All I have done is put it back together and it's working.

I thought it might have been the diverter pin not extending far enough but I could always hear the micro switch clicking on. I have a spare diaphragm so will change it if this happens again, just in case it is that.

Fingers crossed it will keep working.

I'll post back if it goes wrong again (of course, it will die one day).

Thanks very much for your expert help. Kept me looking.

Now for that hot bath!

 

[diamondgas]

Glad to see we're in the right place by sounds of it Andrew! I've had micro-switches be fine initialy but the more you depress them the more the resistance increased. Glad to be of assistance ...

 

[andrewedmondson]

Well, that didn't last long.

I tested the thermistor and found the resistance to be 1.5 kOhm so am replacing this, just in case.

I excluded this before because I was getting 5V across the DHW switch. But now I am getting 0V.

I'll let you know how it goes.

 

[gasbags]

Any more news on this? I am working on a Halsteads Gold everything appears to do what it should but when I run the hot water I cannot seem to get any voltage to start the pump running. If CH is on it cuts out. Occassionally water demand will fire boiler. Changed PCB today but problem persists. Started as a job - now seems more like a hobby trying to fix this. Both microswitches appear fine. Thermisters replaced. Wiring looms checked. Pins operating correctly. CH perfect.

 

[andrewedmondson]

Any more news on this? I am working on a Halsteads Gold everything appears to do what it should but when I run the hot water I cannot seem to get any voltage to start the pump running. If CH is on it cuts out. Occassionally water demand will fire boiler. Changed PCB today but problem persists. Started as a job - now seems more like a hobby trying to fix this. Both microswitches appear fine. Thermisters replaced. Wiring looms checked. Pins operating correctly. CH perfect.

Yes, it turned out to be the thermistor yet again. Seems they only last a few years.

Just noticed that you replaced yours.

Have you cleaned the heat exchanger?

 

[gasbags]

Yes - cleaned plate heat exchanger. Prior to that the burner was cutting out every few minutes. Had cleaned system with X800 and much of the rubbish had gathered in the PHE. Although the fault seems electrical I'll probably strip the hydraulics down again and replace the DHW thermister in case it has an intermittent fault.

Been through the whole thing with Glen Dimplex. Everything gave the voltage and readings expected. Swopped microswitches and problem still persists. Strangely enough with water demand and boiler not firing I tested voltage to pump which was nil then moved the pump speed to 1 and back to 2 and pump started & boiler fired. However I think that this must have just been coincidental. Can't seem to repeat it.

 

[andrewedmondson]

I used two chemicals to clean the heat exchanger: ordinary limescale remover and hydrochloric acid. I left it to soak overnight each time. I also flushed the system.

 

[glenno1]

You may have checked this but is the diverter spindle staying up or dropping off slowly

 

[gasbags]

I have noticed that occassionally with CH on and a demand for hot water the burner just remains lit. I would have expected a proper reignition sequence - ie burner lit for CH - demand for water - burner shuts down momentarily then ignition sequence commences to heat water. On other occassions the demand for hot water just shuts off the CH burner. When demand stops boiler reignites for CH. Diverter spindle appears to operate correctly with CH and when burner does fire for water. When the water demand does not fire the boiler, the horizontal pin works the microswitch but does not bring on the pump and subsequently the vertical pin does not rise to operate the primary flow switch.

 

[gasbags]

Sorted - finally a combination of HW thermister, split diaphragm and poor connection in wiring loom. Rubber diaphragm and thermister were only replaced 6 months ago. Bit of an expert on the Finest Gold now! I'm determined to keep this old boiler going for another 10 years.

 

[glenno1]

learning by experience good on ya