Renewable Heating Hub Heat Pump Forums

Search with Wattson
Forums
Renewable Heating
Thermostats, Volumi...
Why do we need pres...
 
Notifications
Clear all

Joining the Renewable Heating Hub forums is completely free and only takes a minute. By registering you’ll be able to ask questions, join discussions, follow topics you’re interested in, bookmark useful threads and receive notifications when someone replies. Non-registered members also do not have access to our AI features. When choosing your username, please note that it cannot be changed later, so we recommend avoiding brand or product names. Before registering, please take a moment to read the Forum Rules & Terms of Use so we can keep the community helpful, respectful and informative for everyone. Thanks for joining!

Why do we need pressurised systems?

 
Thermostats, Volumisers, Buffer Tanks, TRVs, Pumps, Piping, Valves, Radiators & Controls
Last Post by AllyFish 11 months ago
7 Posts
4 Users
1 Reactions
1,188 Views
RSS
Toodles
 Toodles
(@toodles)
Famed Member Contributor
Joined: 4 years ago
Posts: 2825
Topic starter 31/07/2025 4:13 pm   [#2405]

Having had a second occasion where the system pressure for the heat pump dropped to zero (under investigation at present) I go to wondering:

Why do we need a pressurised system in the first place? I have always assumed that a positive pressure is used to ensure a constant supply of water to the pump(s) thus reducing air bubbles which would be purged from the system during circulation and possibly also to avoid risk of cavitation in the pump impellers.

Have I summed it up correctly or am I nowhere near the truth - is there something else I have not thought of perhaps?

Curious Toodles.


Toodles, heats his home with cold draughts and cooks food with magnets.


   
Quote
 IaAck
(@iaack)
Trusted Member Member
Joined: 3 years ago
Posts: 60
31/07/2025 6:04 pm  

A question for Inspector Watson?



   
ReplyQuote
Toodles
 Toodles
(@toodles)
Famed Member Contributor
Joined: 4 years ago
Posts: 2825
Topic starter 31/07/2025 6:48 pm  

@iaack I enquired of Wattson and the reply was very much along the lines of that which I surmised Holmes.


Toodles, heats his home with cold draughts and cooks food with magnets.


   
ReplyQuote
 IaAck
(@iaack)
Trusted Member Member
Joined: 3 years ago
Posts: 60
31/07/2025 9:38 pm  

@toodles, touché chez. /\



   
ReplyQuote
 Old_Scientist
(@old_scientist)
Honorable Member Member
Joined: 2 years ago
Posts: 452
02/08/2025 12:48 pm  

Posted by: @toodles
↑

@iaack I enquired of Wattson and the reply was very much along the lines of that which I surmised Holmes.

@toodles Is that because the AI has searched the forum for information, and has found and paraphrased your own question and assumptive reply back to you, reinforcing your own assumptions (which may well be correct). Just surmising 🤣 

 


Samsung 12kW gen6 ASHP with 50L volumiser and all new large radiators. 7.2kWp solar (south facing), Tesla PW3 (13.5kW)
Solar generation completely offsets ASHP usage annually. We no longer burn ~1600L of kerosene annually.


   
ReplyQuote
Toodles
 Toodles
(@toodles)
Famed Member Contributor
Joined: 4 years ago
Posts: 2825
Topic starter 02/08/2025 2:11 pm  

@old_scientist If that were the case (and it might well be the case I suppose!) perhaps Wattson would be a bestie to a certain President 😉. Oops, Sorry! No Polyticking! Toodles.


Toodles, heats his home with cold draughts and cooks food with magnets.


   
ReplyQuote
 AllyFish
(@allyfish)
Prominent Member Contributor
Joined: 4 years ago
Posts: 520
05/08/2025 10:16 am  

A good question @toodles. My old open thermal store and oil boiler chugged away quite happily, if expensively, unpressurised. But the header tank was sat right on top of the thermal store in the airing cupboard, with stagnant water sitting at a cosy 30-35degC breeding and growing all manner of questionable organic produce inside it. 🤢 

Pressurisation and sealed systems eliminates the crusty & stinky stagnant header tank issue, and almost completely eliminates risk of pump cavitation. There's a net positive pressure at the pump suction inlet far higher than the minimum the pump requires, and at all points in the pipework system for that matter, making pump or system cavitation anathema. So it doesn't really then matter where in a sealed system the circuit the primary and any secondary pump are placed - they'll do what they do, pumping water. It also usually means a quieter running system with less air entrainment & gurgling.

A sealed system eliminates many corrosion risks. Air in systems promotes internal corrosion. Corrosion needs an oxygenated environment to thrive. No air = no corrosion, theoretically.

And yet installers still do strange things, such as fitting auto air valves on sealed pressurised systems. Open system + auto-vent - yes. But sealed system + auto-vent, er, why? Over time the vent will open, and pressure will be lost. I much prefer a manual air vent, which I can open up to let air escape and then check the system pressure on the gauge and top up slightly with the filling loop if need be. A month or two after system filling no more air separates out and, provided the system is holding pressure, the manual vent never needs checking.


This post was modified 11 months ago by AllyFish

   
👍
1
ReplyQuote
Forum Jump:
  Previous Topic
Next Topic  
Share:

SPONSORS

Join Us!

Installer Finder

Degrees of Separation

Latest Posts

SPONSORS

Click to access the login or register cheese
Protected By
Shield Security PRO