Pressurised Heating System Losing Pressure
Discussion
Had similar with our 15 yr old combi. Pressure dropping and kept losing dhw and getting hot rads at the same time. Had the main heat exchanger and dhw exchanger replaced along with diverter valve service. Fixed all issues, hw flow rate is up and quieter to boot. All done for less than 1/5 the cost of a new boiler.
robwilk said:
I had a lot of problems with my heating system last year losing pressure, I found a small leak and sorted that out but the pressure still dropped over a few days , I had the boiler people out and they said it was my system leaking I have whole house underfloor heating so miles of pipework.
I eventually closed off the flow and return valves under the boiler and the pressure was definitely leaking via the boiler so i called them out again and showed them the drop test and the boiler man said he would look at the heat exchanger but doubted it was that as the boiler was still quite new.
Anyway on stripping it down it was caked in scale as it leaked into the combustion chamber and the water was evaporated by the flames of the boiler.
So check by closing off the boiler from the system for a while and see if the boiler or the system drops in pressure at least you have an area to look at.
I was hoping to avoid shutting off parts - wife / kids moaning it's cold but it'll narrow things down.I eventually closed off the flow and return valves under the boiler and the pressure was definitely leaking via the boiler so i called them out again and showed them the drop test and the boiler man said he would look at the heat exchanger but doubted it was that as the boiler was still quite new.
Anyway on stripping it down it was caked in scale as it leaked into the combustion chamber and the water was evaporated by the flames of the boiler.
So check by closing off the boiler from the system for a while and see if the boiler or the system drops in pressure at least you have an area to look at.
I'll put them together in correct order:
Air is compressible, water is not. When the water expands (because it's hot) it uses the EV to expand into and compresses the air bag in there, when it's cold the opposite happens, this means the system is always pressurised.
You need to find out exactly how to top up your EV with air and how much (pressure) it needs. You may have to drain off some water to do this and will usually need a tyre pressure gauge and bike pump.
V8RX7 said:
227bhp said:
What are you topping the system up with when it loses pressure?
Water by the filling loopBusterbulldog said:
The water is replacing the lost air in the expansion vessel.
You can google it for explanation, there are even guides on Youtube. The expansion vessel (EV) is basically a metal container with a balloon (diaphragm) in it, the balloon is supposed to be filled with air (at a certain pressure dictated by the boiler maker). What you have inadvertently done by constantly using the filling loop is fill the EV with water and squash what is left of the deflated balloon.Air is compressible, water is not. When the water expands (because it's hot) it uses the EV to expand into and compresses the air bag in there, when it's cold the opposite happens, this means the system is always pressurised.
You need to find out exactly how to top up your EV with air and how much (pressure) it needs. You may have to drain off some water to do this and will usually need a tyre pressure gauge and bike pump.
55palfers said:
I have the same problem. We had two extra rads fitted last year. Not sure if the plumber put in a bigger expansion vessel though.
Almost every day I have to top up the system with water.
It seems to be producing more condensate too.
Plumber just left.Almost every day I have to top up the system with water.
It seems to be producing more condensate too.
He re-pressurised the (flat) pressure vessel and now all is toasty.
Nice chap, interested in old cars too. Has a couple of Cosworths. Mk3 Escort and Sierra.
£60 and a cup of tea.
227bhp said:
You can google it for explanation, there are even guides on Youtube. The expansion vessel (EV) is basically a metal container with a balloon (diaphragm) in it, the balloon is supposed to be filled with air (at a certain pressure dictated by the boiler maker). What you have inadvertently done by constantly using the filling loop is fill the EV with water and squash what is left of the deflated balloon.
Air is compressible, water is not. When the water expands (because it's hot) it uses the EV to expand into and compresses the air bag in there, when it's cold the opposite happens, this means the system is always pressurised.
You need to find out exactly how to top up your EV with air and how much (pressure) it needs. You may have to drain off some water to do this and will usually need a tyre pressure gauge and bike pump.
Oh - I didn't get that from your posts - AFAIK filling to the same pressure each time doesn't collapse the balloon. Air is compressible, water is not. When the water expands (because it's hot) it uses the EV to expand into and compresses the air bag in there, when it's cold the opposite happens, this means the system is always pressurised.
You need to find out exactly how to top up your EV with air and how much (pressure) it needs. You may have to drain off some water to do this and will usually need a tyre pressure gauge and bike pump.
However I'm happy to try anything so I have just checked and with zero pressure in the system the old vessel had the factory stated 1bar but I hadn't realised the new vessel was preset to 1.5 bar.
I have now reduced that to 1 bar but it doesn't make sense with the pressure readings I was getting.
To recap - I should have 1bar cold with max circa 2bar hot. (I had 2.5 bar after fitting the new rads)
Immediately after fitting the (1.5 bar) new vessel the system only reached 1.25bar hot.
That makes no sense as the new vessel being pressurised to 1.5 bar wasn't taking up any of the expansion which presumably means I do have some air pockets (taking up the expansion) in the pipework as I have kept bleeding the rads with no air being present the vast majority of times.
Due to my house being very "bottom heavy" with a dual circuit system and bedrooms on both floors the pipework is complex.
I'll try running it at a 1.5 bar and see what happens (hoping to dislodge the air)
V8RX7 said:
227bhp said:
You can google it for explanation, there are even guides on Youtube. The expansion vessel (EV) is basically a metal container with a balloon (diaphragm) in it, the balloon is supposed to be filled with air (at a certain pressure dictated by the boiler maker). What you have inadvertently done by constantly using the filling loop is fill the EV with water and squash what is left of the deflated balloon.
Air is compressible, water is not. When the water expands (because it's hot) it uses the EV to expand into and compresses the air bag in there, when it's cold the opposite happens, this means the system is always pressurised.
You need to find out exactly how to top up your EV with air and how much (pressure) it needs. You may have to drain off some water to do this and will usually need a tyre pressure gauge and bike pump.
Oh - I didn't get that from your posts - AFAIK filling to the same pressure each time doesn't collapse the balloon. Air is compressible, water is not. When the water expands (because it's hot) it uses the EV to expand into and compresses the air bag in there, when it's cold the opposite happens, this means the system is always pressurised.
You need to find out exactly how to top up your EV with air and how much (pressure) it needs. You may have to drain off some water to do this and will usually need a tyre pressure gauge and bike pump.
However I'm happy to try anything so I have just checked and with zero pressure in the system the old vessel had the factory stated 1bar but I hadn't realised the new vessel was preset to 1.5 bar.
I have now reduced that to 1 bar but it doesn't make sense with the pressure readings I was getting.
To recap - I should have 1bar cold with max circa 2bar hot. (I had 2.5 bar after fitting the new rads)
Immediately after fitting the (1.5 bar) new vessel the system only reached 1.25bar hot.
That makes no sense as the new vessel being pressurised to 1.5 bar wasn't taking up any of the expansion which presumably means I do have some air pockets (taking up the expansion) in the pipework as I have kept bleeding the rads with no air being present the vast majority of times.
Due to my house being very "bottom heavy" with a dual circuit system and bedrooms on both floors the pipework is complex.
I'll try running it at a 1.5 bar and see what happens (hoping to dislodge the air)
How do you know what the EV pressure is? How did you measure it and at what times?
Write a full and frank explanation about what you have done, how you did it and what the results were. You must have learned how to do this at school?
Edited by 227bhp on Tuesday 13th December 11:20
227bhp said:
Half of your story is missing, don't ever get any ideas about being a novelist.
How do you know what the EV pressure is?
How did you measure it and at what times?
How do you know what the EV pressure is?
How did you measure it and at what times?
Did you pass comprehension ?
V8RX7 said:
I have just checked
and with zero pressure in the system
the old vessel had the factory stated 1bar
the new vessel was preset to 1.5 bar.
Measured about 1 minute before I posted, with a pressure gauge.and with zero pressure in the system
the old vessel had the factory stated 1bar
the new vessel was preset to 1.5 bar.
We have had this issue twice before, system loosing pressure after a day or so. Both times it turned out to be a joint that wasn't fully tight. It was tight enough for the leak to be measured in drips/hour - ie water/dampness long gone when the heating is on, but not so tight to maintain pressure. Both times there were signs of gunk below the joint though.
One was a TRV joint to radiator that i 'nipped up' tight, the second was on the filler valve connection to the system pipe. Again nipped up tight & seemed to sort the problem.
It could be a bleed valve not fully tight, or any other joint in the system being just shy of 'correctly' tight.
I'd be tempted to go round everywhere you can & check for *any* signs of residue/gunk from your system (even if dry to the touch) and nip them all up slightly.
One was a TRV joint to radiator that i 'nipped up' tight, the second was on the filler valve connection to the system pipe. Again nipped up tight & seemed to sort the problem.
It could be a bleed valve not fully tight, or any other joint in the system being just shy of 'correctly' tight.
I'd be tempted to go round everywhere you can & check for *any* signs of residue/gunk from your system (even if dry to the touch) and nip them all up slightly.
It seems to be mostly solved...
I measured the amount of water I had to drain to take it from 1bar to zero as 4 litres which would be quite a leak (it may be a bit less if it leaks out rather than being drained)
After lowering the new EV pressure to 1 bar and refilling the system to 1.2bar I heard a few gurgles and managed to bleed some air out of two rads (and refilled to 1.2)
This morning it's 1 bar so only dropped 0.2 in the night.
I measured the amount of water I had to drain to take it from 1bar to zero as 4 litres which would be quite a leak (it may be a bit less if it leaks out rather than being drained)
After lowering the new EV pressure to 1 bar and refilling the system to 1.2bar I heard a few gurgles and managed to bleed some air out of two rads (and refilled to 1.2)
This morning it's 1 bar so only dropped 0.2 in the night.
My pressured system was running fine until a couple of weeks ago when we had the lounge plastered meaning I had to take the two lounge radiators off. Since refitting and repressuring, the system loses pressure over about 24 hours. We did have water dripping out of the external overflow pipe but the plumber came and said that was due to the air gap missing - he's put the air gap back in and there is no longer any water dripping from the external overflow. But still the CH system loses pressure. Once I repressure the system, one of the upstairs radiators always has a lot of air in it. So I am stuck in a 24-36 hour cycle of:
- central heating doesn't come on
- go in to loft, see pressure needle on red tank is on zero, turn taps to repressure to 1 bar
- central heating comes on
- check rads, one upstairs one releases a lot of air
- when system is hot, pressure needle shows about 1.5 bar
- central heating finishes ok
- central heating runs successfully 1 or 2 more programmes
- central heating doesn't come on, repeat above steps
Plumber lives quite a way away and I don't want to disturb him between Christmas and New Year if I can avoid it, is there anything else I can check / do to isolate what the problem might be?
Edit - just to add, the other thing I've done is turn off the valves on the two lounge radiators to isolate them from the system incase I hadn't put them back correctly. I was hoping the pressure drop would stop and then I could bring one rad back on and then the other, to identify which one was causing the problem. But with both rads isolated the pressure still drops, so it's something else (I assume).
- central heating doesn't come on
- go in to loft, see pressure needle on red tank is on zero, turn taps to repressure to 1 bar
- central heating comes on
- check rads, one upstairs one releases a lot of air
- when system is hot, pressure needle shows about 1.5 bar
- central heating finishes ok
- central heating runs successfully 1 or 2 more programmes
- central heating doesn't come on, repeat above steps
Plumber lives quite a way away and I don't want to disturb him between Christmas and New Year if I can avoid it, is there anything else I can check / do to isolate what the problem might be?
Edit - just to add, the other thing I've done is turn off the valves on the two lounge radiators to isolate them from the system incase I hadn't put them back correctly. I was hoping the pressure drop would stop and then I could bring one rad back on and then the other, to identify which one was causing the problem. But with both rads isolated the pressure still drops, so it's something else (I assume).
Edited by 48k on Tuesday 27th December 09:04
V8RX7 said:
Mine's under a year old !
Phone the boiler manufacturer. If the boiler is still within the warranty period, they will come out and fix it.I had Ideal Boilers out the other week on a job with similar issues to yours, apart from fixing the fault, the engineer replaced other wearable items at the same time. All FOC.
To conclude this thread I raised the pressure (when cold) to 1.5 bar and immediately heard air / water moving around the boiler / nearby pipes.
I've run it for a few days and it's now fine.
I'm unsure why having drained it a few times (for various extension works) I've had the issue this time but clearly was air trapped in the system.
Weirdly a friend has the same issue so I'll try similar and see what happens.
I've run it for a few days and it's now fine.
I'm unsure why having drained it a few times (for various extension works) I've had the issue this time but clearly was air trapped in the system.
Weirdly a friend has the same issue so I'll try similar and see what happens.
Gassing Station | Homes, Gardens and DIY | Top of Page | What's New | My Stuff