vaillant turbomaxplus + expanssion vessel prblems

[sneakyg]

Hi

Ive recently had my rads changed and since then ive had a few issues - mainly boiler pressure way to high.

when i set the radiator temp control on the boiler to 'max' the pressure shoots up to +3. The plumber recons that the expanssion vessel needs replacing, but he came to this conclussion without checking or touching anything. I did not have these issues before the boiler was serviced by him and the radiators replaced.

I have reduced the rad temp on the boiler to just under 2/3rds and the boiler pressure gage goes to about the 2 mark (but house doesnt warm up as much )

can anyone shed any light on what could be happening?

 

[simond]

If the water content (ie: size/format) of the new rads is larger then the expansion vessel may be undersized.

More likely the expansion vessel is failing and the air charge is depleted. Turbomax expansion vessels do tend to last around 7 years.......

 

[MANDATE]

To me the expansion vessel would need replacing if the diaphragm was ruptured, meaning there would be no 'air' in the vessel to compress.
The expansion vessel when installed would have the 'air' charged/pressurised to about 0.8bar. This means the whole vessel contains air. When water is heated it expands and the extra volume compresses the air in the vessel and cause a rise in pressure of about 1bar so a boiler would operate say from 1.5bar up to 2.5bar.
If the pressure reaches 3bar, not only does it operate the 'pressure relief valve', it is a clear indication that some of the 'air' charge has been lost over time leave less air to compress.
You can check air pressure in the same way you check car tyres.
You can also recharge in the same way, but the excess water in the vessel must be discharged at the same time.
Correcting the expansion vessel does not fully resolve the problem. The PRV once opened usually does not reseal properly leaving you with a small leak which means a small drop in pressure.
Solution is rectify/replace vessel first, then replace PRV.

 

[sneakyg]

To me the expansion vessel would need replacing if the diaphragm was ruptured, meaning there would be no 'air' in the vessel to compress.
The expansion vessel when installed would have the 'air' charged/pressurised to about 0.8bar. This means the whole vessel contains air. When water is heated it expands and the extra volume compresses the air in the vessel and cause a rise in pressure of about 1bar so a boiler would operate say from 1.5bar up to 2.5bar.
If the pressure reaches 3bar, not only does it operate the 'pressure relief valve', it is a clear indication that some of the 'air' charge has been lost over time leave less air to compress.
You can check air pressure in the same way you check car tyres.
You can also recharge in the same way, but the excess water in the vessel must be discharged at the same time.
Correcting the expansion vessel does not fully resolve the problem. The PRV once opened usually does not reseal properly leaving you with a small leak which means a small drop in pressure.
Solution is rectify/replace vessel first, then replace PRV.

Thanks,
how do i check the expanssion vessel? (as simple as poss please) and is replacing the PRV necessary and easy/cheap?

 

[Peruse]

Look in the FAQs at the top of page, the second post by ChrisR

 

[MANDATE]

somewhere there will be a air valve exactly the same as car or bicycle tyre, where can use a pressure gauge and foot or bicycle pump.
Regarding the PRV: A new one will be clean and in working order.
The cost will vary, Halstead wanted around £15 for the one I needed and eventually I got one for£3.50.
You could try dismantling and cleaning the existing one, but you would need to make a thin 'C' type spanner to undo the head.
You open the valve by turning knob 90 degrees anticlockwise which also raises the knob, the spanner can then be placed under the knob to engage with the slot to undo.
It was only after replacing mine that I realised I could have removed the head for cleaning, leaving the body of the valve in situ.

 

[simond]

I don't understand this MANDATE chap, clearly isn't a heating engineer .

Nowhere does the OP state that the PRV has lifted, so his (her?) advice seems to be based on what he did rather than a solution to the actual problem.

If the pressure is rising rapidly to 3bar then the expansion vessel is either undersized (now that the rads have been changed) or has lost some air charge.

The latter is very likely. If I remember correctly, the turboMAX has the vessel down the back of the boiler, so depending on the mounting of the boiler could be difficult changing it.

Alternatives are, in the short term, drain one rad, shut one end valve and use it as a temporary expansion vessel. Then either replace failed vessel or add non OEM one outside the boiler.

 

[sneakyg]

I have looked and cannot see where the valve is......will i have to take the boiler case/cover off to find it?

 

[Agile]

I think the air cap is at the top back.

 

[sneakyg]

Hi

I located the air cap and pressed, some water gashed out. does this mean that the expansion vessel is completly shot? or can i pump it up as a quick fix?

also is their a way of introducing a new vessel to the system without removing the old one? (im asking as ive been quoted about £300 to replace the exsisting one) and money is tight