Rising pressure/losing pressure

[Happyunited]

Hello. I'm sure this has been covered before but I'm hoping you can help me.

Ravenheat CTI 85 Combi boiler (a heap I know) has been losing pressure for about 4 months now. At first I was topping it up every other day then I just left it because I didn't have it on much over summer. So I'm trying to sort it now. I noticed a few leaks, one on the return pipe and one going to the PHX. Nothing major but leaks cause pressure to drop to ill fix them. They are both fixed and pressure still leaking. I noticed large damp patch at the overflow pipe outside so I was thinking a dodgy PRV, fixed that and although the pressure didn't drop as much (the previous one didn't look great around the seal) it's still dropping.

The facts;
If I fill to 1 bar it will be down about 1/4 bar in 48hrs, roughly. (When using)
The temperature rises quite high when the system is on, 2.5-3ish bar.
I've disconnected the filling loop in case this was leaking and filling the system.
I'm 99.9% sure there is no leaks in the system. It's a small house with no pipes in floors.

I was in my local plumbing merchant today and got speaking to an engineer and he was adamant it was the expansion vessel and to fit an external one. I've had a read and I'm capable of this but I don't want to do this if it's a waste of time, what checks can I do to further confirm the diaphragm is gone in the expansion vessel?

Thanks in advance for your reply.

 

[PrenticeBoyofDerry]

It could be that the expansion vessel just needs recharging.
This would require a pressure gauge and pump compatible with a schrader valve.

One of the first checks for expansion valve failure would be to check for water at the schrader valve when pressed.

 

[Happyunited]

It could be that the expansion vessel just needs recharging.
This would require a pressure gauge and pump compatible with a schrader valve.

One of the first checks for expansion valve failure would be to check for water at the schrader valve when pressed.

Thank you.
Last night when the boiler was cold I disconnected the filling loop and shut off the flow and return valves to isolate the boiler. The boiler was at 1.4bar and this morning it's at 0.5 bar. I've just checked outside and there is hardly any discharge from the overflow, prob a spot the size of my fist.

I had a look last night and that valve isn't easy to get at I'll try it today but if no water comes out does that mean the expansion vessel is OK?

 

[PrenticeBoyofDerry]

Like I said, check the pressure on the expansion vessel complies to that of the value in the manufacturers instruction.
If it lower, then it will need recharging.

 

[Happyunited]

Like I said, check the pressure on the expansion vessel complies to that of the value in the manufacturers instruction.
If it lower, then it will need recharging.

Thanks again.
Here is my boiler, there is a lot of numbers on here. Can you help me determine what my pressure should be?
http://theinitiativegroup.org.uk/fscinitiativedatabase/Ravenheat/CS185ScreenV31pdf.pdf

8 LITRES EXPANSION VESSEL PRE-CHARGE-PRESSURE 0.5 bar ??


Or

SETTlNG THE SYSTEM DESIGN PRESSURE
The design pressure must be a min. 1 bar and max. 1.5 bar. These figures are read off the pressure gauge.
- The actual reading should ideally be 1

bar + the height in metres to the highest point of the system above the base of the appliance (up to a max of 1,5 bar). N.B.: The safety valve is set to lift a 3 bars (30 mt/42.5 psig).

- To lower the system pressure to the required value remove drain point (Fig. 93) or drain on the heating circuit.


Is the expansion vessel pressure the same as the pressure gauge on the front of the boiler?

 

[PrenticeBoyofDerry]

8 LITRES EXPANSION VESSEL PRE-CHARGE-PRESSURE 0.5 bar ??

That is the info you need, the vessel should be charged at 0.5 bar.
If it is charged slightly higher that should be fine.

 

[Happyunited]

That is the info you need, the vessel should be charged at 0.5 bar.
If it is charged slightly higher that should be fine.

Thanks again. I just checked and there is air coming out which I understand is a good sign. Of course by pressing on the valve the pressure dropped to zero. I just need to get a pump but it's near impossible to access the valve to check for air let alone get a valve on there to get air in, I swear it would be easier to fit an external vessel. There is a screw at the top of the vessel that I could unscrew and tilt forward a little to give me more play but I'm worried I'll bend the pipe going in at the bottom.

 

[ianmcd]

Make sure that you open a drain point while pumping the vessel up as it is now full of water and you need to empty it before you can pressurise the vessel

 

[Happyunited]

Make sure that you open a drain point while pumping the vessel up as it is now full of water and you need to empty it before you can pressurise the vessel

Thanks.
Do I need to drain the whole system or would I be OK just draining down the boiler so the pressure reads zero?

 

[PrenticeBoyofDerry]

Just drain the boiler down, you can close the flow and return valves to DCH.

 

[ianmcd]

no you dont need to drain the whole system, drain the boiler till it reads zero and leave the point that you used to drain it open then pump the vessel up and more water will come out whatever point you used to drain the boiler then once the water stops coming out you will start to pressurise the vessel once you get the desired pressure then close the drain point and open the filling loop to pressurise the system and that is you done, if you dont do it like this it will not work you must leave a drain point open as you pressurise the vessel

 

[Happyunited]

no you dont need to drain the whole system, drain the boiler till it reads zero and leave the point that you used to drain it open then pump the vessel up and more water will come out whatever point you used to drain the boiler then once the water stops coming out you will start to pressurise the vessel once you get the desired pressure then close the drain point and open the filling loop to pressurise the system and that is you done, if you dont do it like this it will not work you must leave a drain point open as you pressurise the vessel

Thank you. I was going to cheat and use the PRV to drain the system but it seems I can't do this as I can't leave it open? As far as I'm aware there is only one drain point in the house and that's in the Kitchen, the boiler is upstairs.

 

[ianmcd]

it is possible to use the PRV and some Pros do but the downfall is that it might not seal when you manually open it so you will have to replace it, choice is yours , for an amature I would use the drain point in the kitchen or if there are two people there open the nearest radiator bleed valve and have someone hold a bucket or basin to catch the water that will come out when you start pressurising the vessel

 

[PrenticeBoyofDerry]

Figure 93 in the MI shows the boiler drain cock

 

[Happyunited]

Figure 93 in the MI shows the boiler drain cock

Excellent, thank you. Don't know why I've never noticed this before. Now I need to find a bike pump.