Boiler losing pressure every day, replaced PRV, Gauge not showing high pressure

[a546345]

Ok, I'll do that. I had a container under the outlet of the pipe connected to the PRV, but not a bag. The pipe above it for the condensate continues further away and I didn't expect or see a leak on that pipe.

I'll use your "Tie a bag around the pipe" method which would have confirmed originally that the water was not coming from the PRV.

 

[terryplumb]

Yes mate ,little things like that can throw a keen DIY er off on the wrong track.

 

[John D v2.0]

There is only about 20ml difference between 0 bar and 1 bar pressure. About 20ml comes out of the PRV, and I add 20ml back in.

If that, then your system pressure is below the expansion vessel pressure. This is incorrect.
You need to charge the vessel with the boiler empty and drain open to around 0.2 bar lower than the design cold fill pressure. Then cold fill the system.
You will then have a buffer of water in the EV to cover any minor losses.

Of course the minor losses is another issue, but it shouldn't be so severe.

Ps I've been slated before for pointing out this purely because I'm not a qualifiedqheating engineer, but it's a true fact of how physics works and it's how all the manufactures specify to set it up.

 

[terryplumb]

Where do you think op is losing water from John D ?? Its nowt to do with pressure vessel charge mate .regards terry

 

[John D v2.0]

Where do you think op is losing water from John D

Not a clue I am not aiming to assist the op with that query in my above post, in fact I explicitly said although it's an issue, the effect shouldn't be so severe:

the minor losses is another issue, but it shouldn't be so severe

 

[a546345]

You either have a leak on your pipework / rads ,or within the boiler Internally. To determine which...turn central heating off and allow two hours to cool. Isolate boiler electrically. Pressure to ,1.5 bar. Then close FLOW and RETURN valves at boiler. Leave overnight then check pressure gauge on boiler. If pressure has dropped the problems in the boiler. If pressure has not dropped ,open the flow and return valves. If it then drops its a system leak. Tie a bag over prv pipe outside to rule out any loss via prv.
If pressure is lost within boiler ,assuming no water visible within it ,it could well be the HEX.

I've done this twice now. These are the results from the 2nd test.

6/4 9:30am System filled to 1.5 bar. Boiler power has been switched off for 24 hours. Flow and return valves closed on boiler. Bag over PRV outlet. In Line Flow and return valves on heating circuit also closed.
7/4 9:10am Pressure Gauge has dropped by only 0.1 bar. Open flow and return valves on boiler-No change in pressure gauge. Open in line flow and return-no change in pressure gauge. No discharge from PRV pipe. I can't see any water in the boiler.

Would you expect the pressure to go back up when I opened the valves?

The 1st test was done the day before, and the pressure dropped by 0.25bar. No change in the gauge when opening the valves. The boiler had only been off for 4 hours prior to starting, and I didn't have the bag over the PRV pipe which is why I repeated the test.

 

[Daveydub]

Sounds like it is the boiler. Sometimes it will leak when hot more than when cold. You can either, top up boiler to 1.5, isolate heating circuits, run hot tap for a while to get boiler hot and see what pressure you have lost or,
turn boiler off, top up to 2.5, see if water continues to dribble out of the condense line.

 

[a546345]

Thanks! I isolated the heating circuit and topped up to 2.5 bar at 11:30am this morning.

I repositioned the condensate drain at the boiler end so that it flows into a tray.

At 2pm there were 2 or 3 drops of water in the tray, the pressure gauge had not moved.

At 6pm there was 55ml water in the tray. The pressure gauge has dropped very slightly.

How come the flow in the tray doesn't seem to be consistent?

The boiler has not been powered on for 2 days.

Should I now power it up and run some hot water?

 

[a546345]

Hi Daveydub, reading your post again, I'm not sure whether I should have run the hot water 1st before topping up to 2.5 or not.

I didn't run the hot water 1st, but I am getting water out of the condensate drain.

 

[terryplumb]

If your boiler has not been on , I.e electrically isolated all day ,not even used for domestic hot water from taps. And water is Coming out of your condensate pipework ,that is indicative of a leak in your heat exchanger.

 

[Daveydub]

At 2pm there were 2 or 3 drops of water in the tray, the pressure gauge had not moved.

At 6pm there was 55ml water in the tray. The pressure gauge has dropped very slightly.

water is Coming out of your condensate pipework ,that is indicative of a leak in your heat exchanger.

As Terry says, leaking ht exchanger in boiler. The leak will vary with temperature so air slightly warmer, leak slightly worse. re-connect your condense, leave heating isolated and go & run yourself a nice hot bath. Should see a bit of pressure loss then (when it has cooled).

 

[a546345]

Left CH isolated, ran the hot water then left it overnight with power off. Pressure dropped from 2.5 before I ran the Hot water to 2 this morning

Only other thing to mention is that this boiler has a pre-heat mode for the DHW where it supposedly reduces the time until hot water comes out of the taps. I don't know how it works, but just mentioning in case it is relevant.

I guess time to get some quotes for a new boiler.

Thanks for the help.

 

[ianmcd]

The pre heat cant activate with the power off and if you are getting water from the condensate pipe with the power off then you have a pinholed, call Worcester for a fixed price repair, usually £270 but varies depending on your post code I think but not sure, to buy the heat exchanger will be more expensive

 

[a546345]

Just to close this off, I did get the fixed price repair for £275 a month ago and they confirmed the heat exchanger was leaking, and also replaced the pressure gauge, the air valve and a few other items. If there had been much else that needed replacing then they'd have written it off as beyond economical repair.

So I now have a mostly new boiler.

I've not used the heating yet, but it is holding pressure now!

Thanks for the help.

 

[Mattdog3327]

I agree with terryplumb, split the whole system in half, determine the less expensive (or time consuming) half to repair and isolate this. Test this half, if the fault is here, split it in half again if possible, isolate and re-test. Keep halving the faulty "circuit" It won't take long to narrow down the fault and saves a lot of expensive trial and error. I was taught this for electrical or any fluid circuits, half point technique.