Duo-Tec 28 HE A - Temperamental Issue - Heating won't fire up until hot tap is ran

[Dan124]

Hi Guys,
This is my first post. I've been reading the forum for a good while now.

I have a boiler that's making me scratch my head a bit and I'm hoping for some advice before I go down any particular avenue.

It's a Baxi Duo-Tec Combi 28HE A.
No faults/errors are ever displayed.
In an attempt to fix the issue, a previous engineer has fitted a diverter valve cartridge, diverter motor, and a new PCB.
However, the issue is still present.

This seems to be a temperamental issue that doesn't happen all the time.
When the heating gets up to temperature, the burner turns off. The burner will not fire up again (even though the heating is being called for) until the customer runs the hot tap. After this, when it switches back over to heating ... the burner will come on.
I can replicate this issue while the heating is running by turning the heating dial down and then turning it back up again (but it doesn't always happen).
Opening the hot tap momentarily seems to always remedy the issue.

I don't think it's an ignition issue, because it always fires up when the hot tap is ran.
I have checked the diverter myself and it seems to be working correctly.
The hall effect sensor seems to be operating correctly.

If anyone has any ideas I would very much appreciate the advice.

Cheers
Dan

 

[ianmcd]

Hi Dan and welcome, when the CH is satisfied the boiler cuts out and a timer delay comes in to stop the boiler constantly cycling, some work on a fixed time some use the primary thermistor to tell the burner when to come back on, when you open the HW tap this over-rides the timer delay, obviously the timer delay is sticking, you say it is a new PCB, Some boilers you can fit a jumper and over-ride the timer delay but I have never heard of one on that PCB, if it genuinely is a brand new PCB and not an Ebay refurbished job, I would try a primary thermistor, but I do suspect the PCB

 

[Dan124]

Thank you for your reply Ian.
I will try to confirm the PCB is genuinely brand new, and I will fit a new thermistor. At least they're not expensive.
I will report back when I know more.
Many Thanks!

 

[kevinkan]

dan did you get to the bottom of this mate

 

[ianmcd]

dan did you get to the bottom of this mate

obviously he did and like too many is just happy that the free advice worked, you have to start your own post, Hi-jacking this post wont achieve anything and is against site rules, start a post with your own questions and you will get the help that you need