Water pressure dropping within 1 hour in Hotwater tank system

challengesahead

I have moved to a new property with Therma Evocyl hot water system (tank + combi boiler downstairs).
Since the radiators were not heating up at the top, I bled all radiators which started warming up evenly. Noticed that the pressure on the dial at the tank was almost 0 assuming that there was lot of air in the system. So I re-pressurized by opening the cold water filling tap, upto the max 1 bar (red marker). 
To my surprise it went down back to zero after about 1 hours. And since then I have re-pressurized atleast 5 times. I cannot see any leaks anywhere or patches on the wall/ceilings yet. 
I have got similar system --> https://www.redrow.co.uk/tv/videos/howto/how-to-adjust-your-system-pressure
Can any one comment what is going on? or where should i look next?

thanks

tim_p

If all that’s changed is that you’ve bled the rads then keep bleeding and topping up and see how it goes.  If there is a lot of air coming out then that’s a lot of water to replace. 

[Deleted User]

Check outside to make sure that the boiler safety relief valve hasn't operated. If water is dripping from the pipe or the wall is wet then you have your answer. The reason for the PRV operating can be the sudden pressure created by opening the cold water tap. The valve opens briefly but fails to close properly because the water flowing around the CH system is dirty and full of small iron deposits: the result of radiator corrosion. This link explains more

https://www.advancedheatingplumbing.co.uk/my-boiler-keeps-losing-pressure/

If it is the safety valve then this is a job for a registered gas installer and, most likely, it will be an excluded fault from any boiler warranty or insurance. Sludge builds up because whenever fresh water is introduced into a CH system, corrosion occurs. 

PS:  If the engineer decides that a new PRV is needed then it is worth doing a system drain and refill at the same time. Once the problem is sorted, you can use a pressure can of inhibitor (eg; Sentinel or Fernox) which can be introduced to the system via the cold water filling loop.

challengesahead

The system is brand new, so hoping there wont be rust. will check other things mentioned.

brewerdave

Had a similar problem a few years ago, with a "brand new" combi at my daughter's new flat. Altho it took longer for the pressure to fall.
To cut a long story short ,in the end the manufacturer was "persuaded" to send in an engineer who did a complete strip down and found that there was a pinhole leak on the final stage of the heat recovery from the condense. The water in the system was slowly venting to the low pressure condense drain which was out of sight feeding direct into the bathroom drain outlet!
Took nearly 6 months of visits from the builders plumbers and others to get to the final stage.

macman

It's invariably either the PRV not seating down fully, a damaged or under-pressure diaphragm, or a leak on the CH circuit.  The first two are easy to check, the latter can be a nightmare, depending on the pipe runs and what they are made in.
It could still be the PRV, even on a new install, if the powerflush was not thorough enough and some debris remained in the system. Just tie a plastic bag onto the overflow pipe for 24 hours and see if water collects.

[Deleted User]

If it is a new system then as other have suggested it is probably debris left in the system. It shouldn’t happen but it does as most heating sub-contractors are only interested in ‘quick fit and forget’. A ‘Friday afternoon’ boiler is another possibility.

 I moved in a new build about 2 years ago. The WB boiler was the noisiest boiler that I have ever had. The installer just wasn’t interested in my complaint: it was working! More in hope rather than expectation, I decided to pay the extra for the first annual servicing by a WB HQ engineer. He came armed with a laptop and was able to check all the boiler design/build parameters. He changed the heat exchanger; the fan,  and the syphon tube. The boiler now purrs rather than roars.