Combo Boiler issues

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My son has just bought his first house - has a Ravenheat 780 CSI(T)AAA combi boiler. with RHVT 2 wireless thermostat.

He is complaining that pressure on boiler gauge is fluctuating sometimes at 0.5 bar then when hot it can be 1.5 or even as high as 3 bar.
Plus he says it is often noisy, and sometimes sounds like water running/filling inside boiler, plus although temp control set to 21 degrees (wirless stat) house only gets to 17 degrees and boiler shuts off.

I did bleed the rads and checked wireless stat is correct day/time and programmed for sensible on/off periods.
The main index rad takes ages to get warm, even reducing lockshields on the other rads, and having this one wide open it take a long time to get hot ........... maybe just poor system design.
Only time it will warm up quickly is if you crank all the other rads closed (did it for a test)

Variable head pump is on max speed.


The wireless stat works on 21 degree 'demand' and 17 degree night modes, there is no loss of comms alarm.

Any tips what to look for for combi issues ? ..... never owned a combi.

I have not checked pressure vessel intend to do that tomorrow - if no water coming out of schrader valve can I set pressure with air pump without draining down ? any tips on that.
 
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Blockage in CH system.
Main HXchngr blocked
Faulty filling loop
 
Ah, good old Ravenshite...most likely an expansion vessel issue. Vessel should be recharged with no pressure in the system, but you don't need to fully drain, just release the pressure. Might be a drainoff near the boiler somewhere
 
I can drop pressure to nil easy enough (rad vent) ... .... I'll see if water comes out, and check charge if it doesn't.

Thnx
 
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Blockage in CH system.
Main HXchngr blocked
Faulty filling loop


Fillip loop is working OK ... as it fills it.
Exchanger is another issue though .

Never come across Ravenheat before - their help desk was no help at all
 
I can drop pressure to nil easy enough (rad vent) ... .... I'll see if water comes out, and check charge if it doesn't.

Thnx

You need to leave an open end of some description when charging the vessel otherwise you will not get a correct pressure reading.

Jon
 
U need a powerflush and gas engineer/plumber. To have proper look at your son's CH. your room stat is fine, it calls for heat and shuts off.
Problem is poor circulation/dirty system = to ex vessel going, pump, divert valve etc,
Check the colour of the water in the system.
If the CH was working before so I guess the design is ok
 
I can drop pressure to nil easy enough (rad vent) ... .... I'll see if water comes out, and check charge if it doesn't.

Thnx

You need to leave an open end of some description when charging the vessel otherwise you will not get a correct pressure reading.

Jon


I'll see if there is a vent/drain plug on boiler I can drop pressure and leave open .... else I will open up the bleed valves on the upstairs rads .. that will mean circuit is open and not pressurised. That should then allow me to check the charge on expansion vessel. (0.5bar)
 
I can drop pressure to nil easy enough (rad vent) ... .... I'll see if water comes out, and check charge if it doesn't.

Thnx

You need to leave an open end of some description when charging the vessel otherwise you will not get a correct pressure reading.

Jon


I'll see if there is a vent/drain plug on boiler I can drop pressure and leave open .... else I will open up the bleed valves on the upstairs rads .. that will mean circuit is open and not pressurised. That should then allow me to check the charge on expansion vessel. (0.5bar)

There is a drain point on the bottom of the boiler on the left hand side on the boiler flow pipe just by the pressure relief valve. Isolate boiler and drain from here. Leave a container under it as you will force water out if you need to recharge.

When boiler has drained check the expansion vessel pressure. Standard pressure in these is about 0.5bar. This should be fine for most systems I tend to push it up to about 0.6 though but thats just a personal preference.

Jon
 
For typical boiler like this I would always recommend an air pressure of about 0.9 bar.

The remaining air should be let out of the valve whilst there is still pressure in the system to ensure all the air is let out and particularly let out any water from the air side.

Only then should the pressure in the system be relieved ready to repressurise it.

Tony
 
Thanks .... had looked up it does say 0.5 ... I'll aim for what you advise :)

can you give me a clue where I'll find air pressure valve ? ........... I looking at boiler and so far can't find it .... I have seen plenty of nice red expansion vessels - easy to find. Can I get at it once outer case off ..... it's eluding me

The manual talks about removing boiler from the wall if pressure vessels needs replacing ... or fitting external pressure vessel - but no clue as to where air valve is.
 
Last edited:
can you give me a clue where I'll find air pressure valve ?

Look down the back of the boiler it is angled to the left hand side IIRC not easy to get at but is doable. We have extensions to get to these if needs be

Jon
 
So from above ... down the gap between boiler & wall ? ........... arrrgh
Need stepladder then
 

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