Open vented system, No HW, CH works fine, BAXI 80HE boiler shows Dry Fire after every restart

[fandyman]

Ok thanks @Madrab. So all in all there is nothing wrong with the system apart from the boiler going into DRY FIRE. Could the incorrect/stuck 3 port valve cause the flow/return reversing or no flow issues at the boiler or is it an air lock that could do that?

But then still the boiler works fine heating up radiators and hot water when manually operated with the actuator head off. Baffled...

 

[fandyman]

Just for anyone coming across this topic in the future after manually pulling the spindle to CH and HW few times (leaving it in each setting so I can sense the A and B could warm up on their own) and after doing the tests that @Harry Bloomfield suggested I just turned the power off, screwed the actuator head down and turned the power on back again. With the power on I just did one more cylinder thermostat down to min and back up to 55C (hearing the clicks etc) while everything else stayed the same (boiler gauge setting in the highest band, both CH and HW on the programmer on constant ON) and the boiler does not go into DRY FIRE any more. THE HW is super hot like it was before all the issues started and CH comes on as well so all works now.

Fingers crossed it will remain that way.

 

[Harry Bloomfield]

Just for anyone coming across this topic in the future I just screwed down the actuator head after doing the tests that @Harry Bloomfield suggested and did one more cylinder thermostat down to mi and up to 55C while everything else stayed the same (boiler gauge setting in the highest band, both CH and HW on constant ON) and the boiler does not go into DRY FIRE any more. THE HW is super hot like it was before all the issues started and CH comes on as well so all works now.

That reads as if either the actuator is jamming, or the valve. I would be inclined to seek out spares for them, for when the problem shows up again.

 

[fandyman]

That reads as if either the actuator is jamming, or the valve. I would be inclined to seek out spares for them, for when the problem shows up again.

Yes that is certainly a potential reason. I will do as you suggest and finally enjoy a well deserved bath this evening as last two weeks were a bit tough (immersion heater stopped working too).

 

[Madrab]

3 port valves are notorious for acting up once they get to any decent age - they are regularly getting changed due to the way they commit suicide as they use power to stall themselves @ mid position - eventually the motor/switches/mechanism start acting up/burning out. Better getting it swapped over to S plan if the valve is ever to be replaced.

Even when the system isn't calling the motor can be energised if CH only was the last call, so that eventually causes it to fail. It can be reset easily by powering down or set it to HW only and the valve will return to rest pos (B).

 

[fandyman]

Thanks for your input @Madrab. Can you explain a bit more why S plan would be better to my current Y plan in this instance?

 

[DP]

Look at page45 of the manual
The checks will need carried out with a multimeter

Dry fire in this boiler is lack of water movement which either means pump not pumping, too weak to operate the pedal in the flow switch or flow switch is gubbed.

Heating engineer territory else op would have located the defect by looking at page 45 of manual

 

[DP]

Ok thanks @Madrab. So all in all there is nothing wrong with the system apart from the boiler going into DRY FIRE. Could the incorrect/stuck 3 port valve cause the flow/return reversing or no flow issues at the boiler or is it an air lock that could do that?

But then still the boiler works fine heating up radiators and hot water when manually operated with the actuator head off. Baffled...

I am at a loss to see why the three port valve is being looked at as the cause for dry fire unless the HW port of the valve is blocked

 

[Madrab]

unless the HW port of the valve is blocked

I guess the only issue I've been looking at around the 3 port is that there hasn't been any hot water. If the motor has problems then the valve may never get to open up the HW port properly. I must be honest and say that the dry fire issue was supplemental.

As you suggest though, I can only be no flow - either by an air lock, pump issue or if it's just in HW mode then a closed port

 

[DP]

Rab, no reflection on what you posted. I sometimes read a reply in the post way down after it has been posted and write something that may or may not be relevant. Your advice is always to the point and worth its weight in gold
Furthermore, I am sure you have had this fault too, last dry fire among host of other issues was in a new build near Braehead Shopping Ctre

 

[fandyman]

I am at a loss to see why the three port valve is being looked at as the cause for dry fire unless the HW port of the valve is blocked

That's what I suspected was the problem.

Today is a 2nd day in a row all is working fine. I hope it continues.

 

[DP]

That's what I suspected was the problem.

Why do you think the 3 port is defective?
Valve does not move for hot water, the cylinder stat puts a demand to run the boiler , boiler is getting the demand to run hence it is going to dry fire
Question remains, is the electronics getting the correct signal or is the signal not being applied due to faulty component

I have already posted the page that shows how to locate the defect.

Following link comes to mind. Excuse the language

 

[fandyman]

There was no HW only flow before I took the cover off and manually moved the spindle with power on. I think powering it off and on plus some testing with manual spindle movement looked to at least sort it out temporarily for now.

 

[Harry Bloomfield]

3 port valves are notorious for acting up once they get to any decent age - they are regularly getting changed due to the way they commit suicide as they use power to stall themselves @ mid position - eventually the motor/switches/mechanism start acting up/burning out. Better getting it swapped over to S plan if the valve is ever to be replaced.

Yep, or change it to a MOMO type valve and actuator, which avoids those issues...

 

[DP]

There was no HW only flow before I took the cover off and manually moved the spindle with power on. I think powering it off and on plus some testing with manual spindle movement looked to at least sort it out temporarily for now.

The fact remains, the valve does not apply demand to the boiler during HW mode ie the valve is not powered during HW mode so plays NO part in running the boiler.

Your action is causing a part within the boiler to engage like it should and I strongly suspect that is where the defect is as it is functioning intermittently