Pressure problem - strange behaviour Help and information on all topics relating to your central heating, air conditioning and ventilation issues.

[andy2510]

Hi.

I have a (quite old) Ferroli Optima 201 combination boiler. Everything has been fine until recently. I topped the pressure up to 2 a few weeks ago (I know this is slightly too high!) but over the last few days the pressure gauge has been showing pressure on 3 at rest (when the central heating has been off for a few hours).

Earlier tonight it was making strange vibration noises so I checked the pressure - it was on 2. An hour later with the heating still on I ran a bath, and a little while later heard strange noises from the system. My partner checked the gauge and it was on 0! It was like the system had tripped the pressure gauge and everything was drained!

I noticed there is a small leak in the bathroom radiator near the bleed valve, which doesn't occur all the time strangely, but I can't turn this radiator off as it appears to be the bypass of the system (no handvalve and all other rads on the system have thermostat valves). Also the floor round by this rad was dry when the pressure dropped, and also the peice of tissue paper that was wrapped round the leak area.

Is there something strange going on? I've just refilled the system to 1.5 and tested for 5 minutes - the pressure went up to 4 before I switched off. Is that normal pressure after 5 mins?

I haven't checked the safety valve outlet as I don't know where it's exit point is!!!

Any help would be greatly appreciated.

Thanks in advance.

Regards

Andy

[htg engineer]

Check filling loop is isolated - disconnect and cap if possible.

If the pressure still rises then it'll be a expanion vessel or water mixing causing the problems, it could be mixing through a corroded plate heat-exchanger.

To check the expansion vessel - turn the cold water to the boiler off, run the heating, if the pressure rises drastically then the expansion vessel need re-pressurising or replacing.

If the pressure stays steady with the cold water isolated, then you need to check where the water could be mixing.

[andy2510]

Thanks - I'll try isolating the filling loop first (sounds like a tough job - it's never been disconnected! Or so the previous home owner has said - even the British Gas engineer who serviced the boiler in January didn't say anything about it!!!)

More information on current tests - the pressure was just over 3 this morning about 10 hours after switching the central heating off - running for about 20 minutes now and the pressure is stable at 4.

We have a Homecare Flexi plane (the one where you pay £50 for call-out, but as it's £60 cheaper per year you have to pray it doesn't break down more than once!!!) so if the expansion vessel needs replacing would BG need to do it (I would imagine so!) and why wasn't it spotted on it's service?

[andy2510]

Sorry for double post - I've removed the filling loop and still the pressure is erratic - especially when the hot water is in use while the central heating system is operating.

According to the installation instructions the expansion vessel is outside the boiler casing (?) and/or appears to be optional (again ?). The boiler is situated in a cupboard in the kitchen with no external wall surrounding it.

Wouldn't a corroded plate heat exchanger be spotted on a service less than 2 months ago?

Cheers for your help so far.

[htg engineer]

Have you tried isolating the cold water and running the heating ?

Look down the back of the boiler or in the boiler for a big red drum - this is the expansion vessel.

No a corroded plate heat-ex would not be detected during an annual service. It is not a visual fault, it corrodes inside the heat-exchanger.

[andy2510]

Thanks for your reply.

I haven't been able to test running the heating with the cold water operating as I've been out today and the only valve in this house is the mains valve! I will try this though possibly within the next couple of days.

More information :- the central heating boiler thermostat is set at 60 deg C. I have now located the safety valve exit (it was hiding behind a bench) and while it is difficult to tell after it has been raining, there is definitely a large puddle near it.

[andy2510]

I've isolated the mains water from the boiler (or in other words turned the water off at the mains!! I wish there were more isolating valves in this house!)

Result - pressure rising from 1.5 bar to 3.5 bar and a very warm safety valve pipe.

[htg engineer]

expansion vessel faul then - either needs re-pressurising or replacing.

Have you found the expansion vessel yet ?

[andy2510]

I've found it!!!

How do I adjust the pressure - and which way would I need to turn it?

(Looking at the instructions, the safety valve is triggered at 3 bar pressure)

[andy2510]

I've since realised it's like a tyre cap!!!

Can I use a bicycle pump to add pressure on this vessel, and what pressure should it be at? Would a car tyre pressure gauge be any good?

[htg engineer]

Drop system pressure and lock open the pressure relief valve, attach pump a foot pump is best - and pressurise to 1.0bar.

[andy2510]

Currently trying to get hold of a suitable pump (I don't own a car and so have no use for a normal foot pump - and a bicycle pump is too small!).

Meanwhile while the system drained to 0, the hot water didn't get hot (understandable) and also water started leaking out the Domestic Hot Water drainage outlet. Is this anything to do in relation of the pressure loss?

[andy2510]

Hi again. More info:

When using a tyre pressure gauge to measure the pressure in the valve before we attempted to re pressurise it the reading was 0.

I've noticed there is a second similar thread to this one running at the moment (thanks for the namecheck!) but may I ask for an explanation about how the vessel lost it's pressure and why it had?

Personally not only would I like the solution (which you've helped me so far achieve - a big thank you for that) and to understand that and the method to get the desired result, but I also like to understand the problem and it occurrence as well.

I hope I don't take too much of your time away from other people who need your help!

[andy2510]

Problem seems to be fixed now!

The pressure is a lot more stable and everything is flowing nicely (except for the small leak in the bathroom radiator. :( Oh well - I do have my eye on a nice towel rail if the worst happens in there!)

When running through the first time after re-pressurising the vessel the boiler was making a whiny noise, but as this has now dispersed was this air in the system that was trapped and now gone?

Also the pressure relief valve was leaking - though again this has stopped. What would have caused this?

Many, many thanks with your help htg. You've saved my a lot of money calling out someone who might charge me a packet and still not solve the problem (like my partners brothers former home - same boiler type, same problem but not fixed - everyone was looking for a leak!) or say something else is wrong when it wasn't.

[htg engineer]

Sometimes just abit of debri or muck gets stuck in the seating of the valve, stopping it from closing fully.

If you imagine the inside of the expansion vessel - it is halved with a rubber diaphragm, half filled with air and the other with water, the air is there to take the expansion of the water when hot. With the rubber diaphragm constantly taking the strain, it becomes stretched therefore it may not have lost any air, but needs more air to equalise the pressure - when you re-pressurised the vessel the diaphragm will now be taught again.

Or air could be escaping from the expansion vessel - is there a dust cap fitted to the schrader valve ?

Hope this makes sense