ravenheat boiler woes

[pep]

I have budgeted to replace my ravenheat combi next spring.
However, I think I have a problem with the expansion vessel, the pressure rises to 3 bar from 1 when the c h is put on then the prv lets water drip out . when the system is cold the bar reads 0.
Is it safe to keep topping up for this winter ?
No pressure drop problems in the summer when the ch is not used.
I have 15 radiators in the house.
Can anyone recommend a good quality make/model for my requirements.

 

[compheat]

It does sound like your expansion vessel is faulty. you can check previous post's on this subject. Every plumber will give you different advise on boiler's I use Worcester Bosch Greenstar's and had no trouble but its a minefield out there

 

[pep]

Thanks for youe reply.
I can see from previous posts that the expansion vessel needs (depending on make) beetwen .5-1 bar of pressure pumped into it.
I am mechanically minded so I am trying to get a clear picture in my mind of how the boiler works.
Am I right in thinking that the expansion vessel is 'somewhere' for the water to go when everything hots up ?(expands)
Should it empty itself back into the boiler when cooling ?
By pumping air into it, does this aid this procedure ?
As I have stated, I am hoping to change it in the spring.(THE BOILER)
Would adding an extra (external) expansion vessel be a good idea (£)
to see me through the winter, if putting air into the original (which is almost impossible to get at) is not the answer ?
Also am I right in thinking that to check the pressure in the expansion vessel, the boiler would have to be cold and the pressure on the boiler gauge at 0 bar ?
Would I at this point expect to have water in the ex vessel ?
Thanks in advance for any further insight/advice.

 

[compheat]

Yes you are correct regarding E vessel. fitting an external one is a good idea. and no you shouldn't have water at air valve on E vessel THere is a Diaphgram that keeps the water seperated from the air Its only when the diapraghm rupters that you get water at air valve

 

[chrishutt]

Also am I right in thinking that to check the pressure in the expansion vessel, the boiler would have to be cold and the pressure on the boiler gauge at 0 bar ?

Smart kid! Yes, you're right.

The usual way to get boiler pressure down to 0 is to close isolating valves below boiler and drain the boiler, leaving drain point open. You can then check the EV pressure with a gauge that fits the schrader valve, and pump it up with a bicycle pump.

If the boiler is the highest point in the system, you do not need to close isolating valves. It should be noted that there is a danger of old isolating valves developing a leak if disturbed.

 

[pep]

Thanks to both of you for your input.
I think I will go for fitting an auxiliary ex vessel as when I pressed the needle in the valve it did start to drip.
Can I purchase a universal one ? (non Ravenheat)
Do I need to isolate the original ?
What cost approx are they ?
One last question.
When I purchase my new boiler next year, what would be the ideal btu output to service 16 rads ?
We also have two bathrooms and a downstairs toilet/sink.
I can't see the demand for hot water coming from more than one point simultaneously very often.
However, I do have a mixer shower in one bathroom (the other is electric)
so it may happen occasionally.
Again thanks in advance for any light that is shed......

 

[chrishutt]

Can I purchase a universal one ? - YES, you need 8 litres (standard size) with mounting bracket. Normally cylindrical (near spherical) shape, unless you need it to squeeze into narrow gap or something.

Do I need to isolate the original ? - NO, unless it is leaking water.

What cost approx are they ? - see BES mail order site. Probably £20 including bracket.

When I purchase my new boiler next year, what would be the ideal btu output to service 16 rads ? - output of combi boiler is determined by HW requirement. Heating load is rarely as much (work it out if you like). Suggest 28 kW output for about 11 litres/minute HW flow, although 24 kW would do.

 

[Slugbabydotcom]

I would say 16 rads is a lot for a standard vessel and would be inclined to get one slightly larger. Theres less than £2 basic price difference between the 8, 12 and 18 litre vessels

Click here and search for pressure vessels