No central heating on BAXI DUO-TEC COMBI 24 HE

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Hello everyone,

My home has a BAXI DUO-TEC COMBI 24 HE.

The radiators won't heat up even though the boiler is showing a green light saying they are running. The hot water is still working though.

I've tried bleeding radiators and then pressurising the boiler after but I still have the same issue. The only way I've got the radiators to heat up is by opening the valve on the right, at the back ("heating return" according to manual so im assuming this needs to be open) but leaving this open causes the pressure to raise above safe levels. It went all the way up to 4.

If this is just a simple set up issue then that saves wasting an engineers time and money too.

I've included pictures of when the valve is open but I currently have it closed due to the pressure issue.

Are the valves in the correct position for normal operation?

cW5h0s8.jpeg


gKiulE9.jpeg
 
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CBW

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Yes you need to leave the return open, or it won’t circulate as you’ve discovered. Engage in a local gas safe registered engineer and have your expansion issue (pressure going high) and should all be ok. I’m guessing it’s never been serviced either, so perhaps get this done as well?
 
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The two smaller black valves at the front of the boiler are to fill the system (1 bar is enough pressure when cold)
The larger black valve far right, at the back, is to isolate the boiler from the heating system for maintenance etc, along with its mate far left.
Both these valves must be open for heating to work.
Water should not pass into heating system and increase pressure with filling valves closed (as shown in pic)
Sometimes those valves become stiff, and the plastic levers spin on the shaft instead of actually turning them.
 
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Thank you both for the quick reply.

I'll get on the phone to an engineer. Just wanted to make sure I was understanding the manual correctly.
 

HH1

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The pressure will rise to 4 bar then the safety valve will lift.
If you switch the boiler back off the pressure probably comes back down to below 0.5 bar, resulting in a need to top up the pressure again (?) perhaps.

Have you tested your expansion tank?
From your description it sounds like there may be a problem in that area.
At the top of the expansion tank there is a valve, same style as a car wheel valve.
Remove the cap, and press the valve plunger.... Does air or water come out, or perhaps nothing?

1. If nothing comes out, its lost pressure - get a bicycle pump (or similar) and pump it up to 1 bar.
2. If water comes out, the diaphragm's been compromised - get a new expansion tank and fit it. Cost about £40 for the tank.
3. If air comes out, get a bicycle pump (or similar) and pump it up to 1 bar. - - the problem lies elsewhere.

Very likely #1 or 2

EDIT Oh, if you are just needing to pump it up, relieve the pressure in the water circuit, and do it cold.
 
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The pressure will rise to 4 bar then the safety valve will lift.
If you switch the boiler back off the pressure probably comes back down to below 0.5 bar, resulting in a need to top up the pressure again (?) perhaps.

Have you tested your expansion tank?
From your description it sounds like there may be a problem in that area.
At the top of the expansion tank there is a valve, same style as a car wheel valve.
Remove the cap, and press the valve plunger.... Does air or water come out, or perhaps nothing?

1. If nothing comes out, its lost pressure - get a bicycle pump (or similar) and pump it up to 1 bar.
2. If water comes out, the diaphragm's been compromised - get a new expansion tank and fit it. Cost about £40 for the tank.
3. If air comes out, get a bicycle pump (or similar) and pump it up to 1 bar. - - the problem lies elsewhere.

Very likely #1 or 2

EDIT Oh, if you are just needing to pump it up, relieve the pressure in the water circuit, and do it cold.
Disregard everything in this post , it is totally wrong
 

HH1

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Ian,
Would you care to clarify WHAT, in your opinion is wrong with the statement I made.

Or is it that I have gave too much info away?

EDIT:-
And if the people that thanks and likes the post want to contribute as well, I would be interested in the opinions, and explanations of what is wrong with the post I made.

Thanks.
 
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HH1

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Oh, I must add...

I had a similar problem with my boiler, which was the same make and model.....

Although didn't have the circulation problem due to the closed return valve, but as someone earlier pointed out, the valve should be open.

My problem involved a rise in pressure during operation.
When switched off and allowed to cool the radiator pressure had fallen to below the "low Pressure" cut off point, therefore needed topping up with the filling line.

Upon checking the expansion tank valve, there was indeed WATER coming out of the valve.... I.E. the diaphragm had gone !!!
Quick check on ebay got me a NEW expansion tank.
This was duly fitted.
VERY easy job to do, not requiring any "specialist" assistance.

Job done , boiler back on line and working as it should....
 
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DP

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Upon checking the expansion tank valve, there was indeed WATER coming out of the valve.... I.E. the diaphragm had gone !!!

Not always a sign of EV failure.
 

DP

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Hello everyone,

My home has a BAXI DUO-TEC COMBI 24 HE.

The radiators won't heat up even though the boiler is showing a green light saying they are running. The hot water is still working though.

I've tried bleeding radiators and then pressurising the boiler after but I still have the same issue. The only way I've got the radiators to heat up is by opening the valve on the right, at the back ("heating return" according to manual so im assuming this needs to be open) but leaving this open causes the pressure to raise above safe levels. It went all the way up to 4.

If this is just a simple set up issue then that saves wasting an engineers time and money too.

I've included pictures of when the valve is open but I currently have it closed due to the pressure issue.

Are the valves in the correct position for normal operation?

cW5h0s8.jpeg


gKiulE9.jpeg

With heating demand, does the burner light come on?
At what temperature does the burner light go out?
 

HH1

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Not always a sign of EV failure.

Thanks for adding your comment.

Where else would the water come from in the "air" side of the tank?
I'm asking cause I'm interested.

Anyways, I will have to reword my statement then...
If there is water coming out of the air valve, it is a possible sign of the diaphragm failure in the expansion vessel.
 
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Nothing at all is wrong HH1 with your above statement.
The ExV is always your first check with this type of fault.
Just keep it to yourself though or the "Gas Police" will come a knocking on your door!!:sneaky:
 

DP

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It is not uncommon to find some water in certain boiler vessels.

a failed diaphragm Will be punctured and fail to hold air which will vent through boiler air vent and heard as ‘boiling water’ noise and no charge

On a different level, air can ingress through plastic pipe and merge with water ( hence barrier pipe for heating systems)* I wonder if it was possible to get some water transmission through membrane to air side. It is strange to find this happening to certain boiler expansion vessels not all.

* Barlo pipe was worst for this happening
 
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CBW

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And if the people that thanks and likes the post want to contribute as well, I would be interested in the opinions, and explanations of what is wrong with the post I made..
I don’t know any domestic boiler where the pressure relief valve operates at 4bar, and as per @DP, not always a sign of a ruptured vessel with water at the schrader valve.

A thanks on a post, is generally because the information provided is of use and generally accurate.
 

HH1

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COOL,
Thanks for replying folks.

servotech - Don't want any gas police knocking on the door. But some basic checks can get problems resolved quickly, or at least give an indication as to repair time and cost. Is this repair in need of a gas safe technician as it's on the water side on the particular baxi boiler? I didn't think it would have.... but I may have been mistaken?

DP - on the baxi model mentioned in the OP's post, there is only one connection of the expansion vessel to the radiator circuit, therefore only one way "in" for the water. The schrader valve is open to atmosphere, with no connection to anything else. So I have a failure to see where water in the "air" side could come from. It's a direct copper pipe connection to the expansion vessel from the radiator circuit. BUT, thanks for info.

CBW - The 4 bar.... may be 3 bar setting for the relief valve, but original poster quoted 4 bar on the gauge... so one reading or another is obviously faulty. the relief valve may state 3 bar.... how accurate is that, or is it a general vicinity of 3 bar.... same goes for the gauge on the boiler. I think the "don't know of any.....at 4 bar" is "nit-picking", as the OP's stated it's 4 bar on his gauge.

On another note..... the "thanks" on the post referred to the "Thanks x1 that ianmcd got the his "disregard..bla, bla, bla... " post, in response to my post that was trying to help the OP's problem.
So... the information supplied by jammcd has some credence? It was HIS post that was "Thanked". Not mine.
The information provided by myself would have some help to the original poster, and any other person experiencing the same problems.

Still waiting on ianmcd to CLARIFY what he is referring to ... well the full post as he said that was totally wrong?. Really? I WILL CALL THIS ONE *******S..
someone is either trying to get a "rise" or hasn't got a clue about the particular problem....

AND still waiting on ALTERNATIVE EXPLANATIONS as to what is could be...

wish the OP would get it sorted and get back to us with the solution that was found.
 
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