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Thermal expansion is the tendency of matter to change its shape, area, volume, and density in response to a change in temperature, usually not including phase transitions.Temperature is a monotonic function of the average molecular kinetic energy of a substance. When a substance is heated, molecules begin to vibrate and move more, usually creating more distance between themselves. Substances which contract with increasing temperature are unusual, and only occur within limited temperature ranges (see examples below). The relative expansion (also called strain) divided by the change in temperature is called the material's coefficient of linear thermal expansion and generally varies with temperature. As energy in particles increases, they start moving faster and faster weakening the intermolecular forces between them, therefore expanding the substance.

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  1. L

    What threads for flexi pope to expansion vessel?

    Hi all, I need to order a flexible pipe to connect this vessel up with. The pressure vessel instructions don't mention the thread size? A 22mm pipe almost fits over the threads so I assume it's 3/4 BSP? Does that sound right? The other end goes to the valve, will a flexi like this...
  2. T

    Why is water flowing through my expansion pipe

    Water is flowing through my central heating expansion pipe even when cold with the pump running. Hot water flows through it when the system is heated. Pump has been replaced but still happens
  3. Andrew Garrett

    Worcester Bosch i30 Greenstar PRV and Expansion Chamber replacement

    Hi all What kind of time is required to replace the Pressure Relief Valve and the expansion chamber in a 6 year old Worcester Bosch i30 Greenstar? Is this a 3 hour job? Also what kind of price would be reasonable? I am using a new gas engineer and I want to verify that his bill is fair. I am...
  4. M

    Taking hot water feed from expansion pipe.

    I fitting a new Mira shower in a slightly different position in the bathroom. It’s going to be easier to feed it with cold water from main cold cylinder feed and from a connection to the hot water cylinder expansion pipe. These are just above the shower position. the pipes are both 22mm and I...
  5. C

    Do I need expansion vessels?

    Hi Looking at getting a Worcester Bosch 4000 24kw system boiler and a 210L Ideal tank. A friend showed us their system and they had two expansion vessels, one for the hot water tank and one for the central heating. Thought I'd have a look into the technical side before speaking with plumber...
  6. M

    Stopping pipe expansion noise

    I have a nightmare of a job trying to stop pipe expansion joint noise. There are 28mm copper CH pipes down a landing (at right angles to joists) that's 15-20m long, there are several branches and drops to rads. The joists are notched and felted, and the pipes have "Flexej" axials expansion...
  7. M

    Expansion vessel position

    I see a lot of small 2l expansion vessels fitted horizontally and a few with the water connection at the top, in the legionella advice it mentions having water connections at the base for draining and flushing, also so no debris falls into vessel. From a practical view if the membrane breaks...
  8. F

    Feed and expansion tank/cistern and few general system questions.

    Hi, I've got a leak coming from the loft into a bedroom which I think is caused by water overflow from feed and expansion cistern (see attached one of the photos when I found out the cistern overflowing above the overflow pipe) and one other pipe that has a small drops coming out of it that is...
  9. ollie74

    Boiler Expansion Vessel Question

    Hi, I have a Glow-Worm Easicom 28 boiler and i had to get a new 8 litre EV (expansion vessel) for it, which has arrived. i did check with the seller to ensure the new EV was correct for my boiler and he said it was. the query i have though is, on the original faulty EV, on the sticker, it says...
  10. Crossfingers

    Can a DIYer replace an expansion vessel

    Hi Is it possible for a DIYer to replace an expansion vessel and hose? It's an external grant vortex boiler and from what I've seen online it looks simple enough
  11. D

    Expansion tank location open vented Maxipod

    I'm about to start the plumbing of my house and wanting to use a maxipod with a oil fired boiler and a log stove. But its a single story house. Can i have my expansion tank below the flow and return pipes located in the ceiling? I've did a basic drawing below to show the layout.
  12. P

    Lining old joist notches to prevent expansion noise

    Has anyone tried lining joist notches with a low friction, high temperature resistant material to prevent the bangs when a pipe expands and momentarily sticks on the joist?
  13. C

    Gledhill PULSAcoil 180 Thermal Store - Feed & Expansion Arrangement

    According to the manufacturer's information OV PULSAcoil thermal stores are primarily designed for use with on/off peak electricity but also have two open pipe spigots (NO internal coil) for flow and return from an additional heat source e.g. a heat only boiler. The 180 store comes with a...
  14. R

    Overflow from Expansion tank Dripping

    I hope someone might explain to me why the overflow from the expansion tank drips in the morning for about an hour after the heating fires up, it then stops and does not drip again during the day. I have a fully pumped "Y" system as show on the accompanying drawing the dripping occurs on the...
  15. P

    URGENT Do I need a expansion vessel fitted to my system

    I have just had a water meter fitted and since been told I need a small expansion vessel fitted to my domestic hot water system as the meter will have a NRV in. I have also been told no I don't as my boiler is over 10meters away from the meter and any expansion will be taken up within the...
  16. R

    Why do I have 2 Expansion Vessel

    I have Gledhill 300L unvented water cylinder storage system with Vaillant Boiler. We are using it for UFH and radiators. My plumber has fitted 2 expansion vessels 1) Zilmet - 18 Litre Red Heating Expansion Vessel & Sealed System 2) MULTIFUNCTIONAL TANKS WITH REPLACEABLE MEMBRANE Why has he...
  17. M

    Expansion vessels and charges

    What causes an expansion vessel to loss it's charge and at what rate would you expect it too? Thanks
  18. M

    Expansion vessel hose

    Do many merchants sell 1 meter long 3/4 male to 3/4 female. The 3/4 male screws in to the composite valve and the other end the expansion vessel. I presume came supplied with the composite valve. The flexi is leaking.
  19. J

    Advice combi boiler plumber says can't fix expansion vessel/access it?

    Hi there, I was wondering if anyone could advise if I should get a different plumber for a 2nd opinion. Basically, my combi boiler is in my attic. It is overpressurised at the moment and the overflow pipe always drips. I had a plumber round, he seemed good and honest and knew the neighbour so...
  20. R

    Hot Water Tank Expansion Vessel Question

    Am I correct in saying that the capacity of an expansion vessel as written on the appliance data label is the capacity of the water compartment alone and excludes the air compartment capacity? Thanks
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