100 Random Plumbing Questions Part 2

[WaterTight]

To be less off-putting, I'll only post 3 at a time from now on. Estimated Time Of Thread Series Completion: Dec 2020

8. Combi's I believe aren't best for places where simultaneous demands on hot water occur because no stored water is utilised, all of it being heated instantaneously. But did I remember wrongly that you can only get a finite number of subsequent uses from a combi? Say 2 showers one after another. If this is so (which it may not be) why is it? Instaneously heated water should just continue to be heated as it's called for shouldn't it?

9. In a friend's house (possibly just overnight or possibly just not heard over background noise of day) they get a dull rhythmic chinking noise like tapping a radiator with a biro-point which occurs once every few hours and either starts off as one tap every second for a few seconds and then speeds up briefly before stopping or takes the opposite pattern of starting faster then slowing down. It sounds like it's under the floorboards leading to a rad but that's a guess. Am I right in guessing that a pipe is moving as heated water passes through it and it is either tapping against another pipe (metallic chinking sound) or against a nail or it's loose pipe clip? And if so, would the first port of call be the fairly drastic action of putting on the heating, removing the furniture and bed, lifting the floorboards and hoping to catch the dancing pipe red handed?

10. I remember learning in college that occassionally some selected rads can get hot when only hot water is being called for because of an unwanted effect occuring, unwanted partial circulation of a sort. What is this effect called? And why wouldn't the trusty port valve(s) prevent it getting that far?

 

[justlead1]

Q/8 Yes they have limited delivery of hot water. But i thought that they will give a continuous supply.
9.Expansion and contraction is the cause of the noise. It can be most difficult to stop this occurring. The most common situation, being where pipes change direction and lack any space to lengthen when heated. Things like hole in flooring for a rad tail to tight.
10. Will happen when the returns are commoned.

 

[WHPES]

9, hard to identify the source - you have to try and narrow it down by pressing on the pipe with your fingers as it's doing it to try and find the source. Even then it's difficult as the sound transmits through the copper pipe. A quick fix (but only temporary) is to spray some dry film PTFE where the pipes pass through the floorboards etc.

10, pay attention to design when installing a system.

 

[Renewable M]

Hello matey.

Q8, oil combis (good ones tend to keep a store of 50 litres of water hot, for passing through the plate heat exchanger, so you have 'on tap' (no pun intended) abundant hot water while the burner can catch up and re-warm the heavy boiler shell.

Q9. I have this under my landing. I had a look. The joists are notched and the pipes sit in the notches. When they get hot they apparently move that tiny tiny amount and make that click sound, of varying speeds like your example.

10. It should not be possible for heated system water to gravitate to one end of a near by rad...... but as WHPES says, it's down to laying the baby out. I have seen it where the return from the upstairs rads comes downstairs to the cylinder return....... and the residual heat going back to the boiler gravitates UP the RETURN to the radiator in the room above.

Hope this helps.

 

[Bernie2]

As far as I am aware you can get instant hot water for as long as you like or should I say this with a few proviso?

a. The combi uses gas like its going out of style and can rob gas off other appliances, when in the dhw mode. If you have a cooker going it may very well rob the gas then when the combi goes back to central heating mode the gas comes back on again to fill the place with gas. Its highly important this is taken into account when sizing the gas supply and where it is taken from.

b. The casings don't half get hot if the combi runs for too long.

I mean two 5 minute showers mean it would be on for 10 minutes at full belt perhaps?
It all depends of course on the heat loss of the casing as to how hot the surrounding area gets.
　
　
9. Usually expansion in the pipe itself. It expands at a fairly uniform rate if conditions are right that is probably why the sound is rhythmical. It could also be a water metre or even the pump or any of the things already put up.
　
　
10 Sometimes depending how its piped out, you can get partial reverse circulation down the return pipework. Possibly the three tee rule is broken.