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

[Johntheo5]

I did that test and yes the roomstat turns off the boiler if TRVs set to 5 and I turn the room stat down to 10C. I then turned it up to 22C again and the boiler switched on. After that I had to turn the TRV down to 0 from 5 and again to 5 and observed the boiler firing again. I checked the CH pump after the test and it was showing 19W (I listened to your advise and change it to CCII which seems to be working fine for now).

Thats looking good, don't order anything just yet if you allready havn't.

Next, put the CH permanently ON but with roomstat at 10C, a few TRVs at 5, then select HW (let the CH ON) and turn up the cylinder stat, does the pump/boiler fire up. Note the pump power.

 

[fandyman]

Thats looking good, don't order anything just yet if you allready havn't.

Next, put the CH permanently ON but with roomstat at 10C, a few TRVs at 5, then select HW (let the CH ON) and turn up the cylinder stat, does the pump/boiler fire up. Note the pump power.

Hi @Johntheo5 . Yes the pump and boiler fire up and the pump power shows 19W as well.

Notice that both tests from today were done with the actuator head taken off from previous investigations (the valve was set manually to mid position).

Should I repeat the tests with actuator head on?

What does it all mean?

 

[Johntheo5]

THere may be nothing wrong with your system!!, but all tests should be done with the actuator head on. For the moment just do the second test, again, and post back.

 

[Madrab]

THere may be nothing wrong with your system

Hope not - if that's the case then there was absolutely no point to 8pg's of this post - the whole reason for this was there was an issue with no hot water when calling for HW, the boiler was dry firing and there was unusual behaviour and it would only work when CH and HW were being called for, according to the errors as per original post #1

 

[fandyman]

The boiler switched on but did not fire (maybe the HW cylinder is already too warm?) I heard the click on cylinder thermostat but had to crank it up to almost 70. But still does not fire for now. The pump is showing 18W.

 

[fandyman]

@Madrab Just spoke to a heating engineer over a messenger re the Y plan vs the S plan and he told me this (without seeing my set up yet):

"... I don't believe there's any main differences between an S plan and a Y plan cause they both got pros and cons between them. With S plan you will need 2 valves so you have 2 chances of either of these valves going faulty. You will probably need a bypass for either this boiler or a next boiler. That will also have component on it that can go faulty, get blocked up, be set up incorrectly etc. The Y plan itself is just basically a one zone valve so you do not need a bypass for this. There's pros and cons between the two - for me whatever you've got you stick with it. Obviously the main difference would be wiring - if they are wired up right they normally work forever the way they should. System wise it's a problem for both so if the system is dirty and got debris in it or sludge or something in it that is foreign (not water) they will both be an issue. You do need a clean system free from debris and sludge..."

What do you say - is he right or wrong?
What is the advantage of S plan?
Do I need a bypass with S plan if the pump is not operated by the boiler (pipe overrun)?

@Madrab Can you advise here please?

 

[DP]

The boiler switched on but did not fire (maybe the HW cylinder is already too warm?)

I am getting blue in the face trying to tell you issue has 99% probability nothing wrong with the what you are looking at
System operation.
Timer switches on to call for heat ( boiler has not seen a demand at this moment in time )
Neither thermostat is calling for heat therefore………( boiler has not seen a demand at this moment in time )
Sometime later HW thermostat calls for heat - now there is demand for heat at the boiler
OR
CH thermostat calls for heat -( boiler has not seen a demand at this moment in time )
Motorised valve moves to close HW port - only now will the boiler get out of bed to get on with the task


Fandyman, the repair of what is happening is a task that will need professional assistance.
What you are trying to comprehend at this moment in time is beyond your reach. Do not be offended, I am not being rude, just realistic.

Some salient points for you are 1. Boiler will not run unless the orange wire on the 3 port is at mains voltage. Forget the rest as it will just muddy the water for you.
2. if now the boiler is firing with pump not running, another fault has been introduced.
3 my money is fault that you originally posted is within the boiler.
4. What you post is being looked at by all the posters who do not have visual of what you are looking at and lot of what you are posting is not relevant
5 fault diagnostics is the only way to get to the bottom of this saga. You appear not to have the tools or the knowhow to do this. Please do not be offended

 

[fandyman]

The boiler switched on but did not fire (maybe the HW cylinder is already too warm?) I heard the click on cylinder thermostat but had to crank it up to almost 70. But still does not fire for now. The pump is showing 18W.

Ok the boiler fired now eventually with the pump showing 18W. All the 3 rads that were put on 5 on TRVs are cold.

 

[Johntheo5]

You are circulating ~ 9.0LPM through the coil which is fairly normal for that ~ 2.8M pump head, the boiler may have been slow to fire because its own stat was still satisfied. If still firing now just programme OFF the CH and see if it continues to fire

 

[fandyman]

I pogrammed OFF for CH now (HW still ON) and the boiler and pump switched off.

 

[fandyman]

Ok now I went to set the cylinder stat to 0C and back to about 65C the boiler fired and pump shows 18W.

@Johntheo5 I think I did not do the last step when I set CH to OFF when the boiler was firing and tried to continue seeing it being fired.

Am I correct here or the boiler should keep firing anyway without the need to go to the cylinder stat to reset it?

 

[Madrab]

@Madrab Can you advise here please?

Apologies @fandyman I completely missed this. There is a great difference between Y and S plans - for every 2 port valve I replace (good qual valve) I replace maybe 3x3 ports. By their very nature 3 port valves burn themselves out much faster than 2 port valves do as they can be powered constantly depending on what was the final call for heat. I have S plan systems that have never had their valves replaced (honeywell), can't say the same about the Y plans - every Y plan I look after (where they haven't been converted) has had the actuator replaced.

Y plan systems (Mid Pos) are no longer recommended as a standard.

All systems these days that don't have an internal/incorporated bypass should have one - it really is best practice to extend the life of the pump and the Main HEX during pump over-run. Yours is an older system but the boiler would normally be controlling the pump. An S plan should have an autobypass yes but once it's set then it can be left alone.

AS far as the system being clean - he's not much of a CH engineer if he tolerates having any system that isn't clean and well maintained.

 

[gazfen]

Get a combi mate.

 

[fandyman]

Get a combi mate.

I was advised I cannot get a combi even if a large one due to the size of the house and two bathrooms.

 

[Johntheo5]

Ok now I went to set the cylinder stat to 0C and back to about 65C the boiler fired and pump shows 18W.

@Johntheo5 I think I did not do the last step when I set CH to OFF when the boiler was firing and tried to continue seeing it being fired.

Am I correct here or the boiler should keep firing anyway without the need to go to the cylinder stat to r

If the cylinder stat was still calling, boiler on, when you switched off the CH then it should have continued to fire until the cylinder stat is/was satisfied.
You might do one last test, CH programmed ON, couple of TRVs opened, HW programmed OFF, turn up the roomstat and see if boiler fires, note pump power.