Any plumbers?

[User6179]

I hate combi boilers. Give me a nice big cylinder of hot water any day

I hate combi boilers as well, it seems the more efficient energy wise they get the more that can go wrong with them and probably in money terms are a lot less efficient than they have ever been .

 

[slowmotion]

But I don't understand how turning the hot water on would help in this situation ?

It wouldn't. The CH circuit is completely separate from the hot water one and the mains cold feed. The only time the CH circuit is connected to mains pressure water is when the CH is initially pressurised. That's just a temporary commissioning operation.

 

[ColinJ]

Getting the water through is not the problem ,7 metres of 15mm pipe holds about a litre of water and by the sounds of your pressure you will be getting a litre every 5 seconds or so , if you turn on the taps full pelt and you are getting more water than the boiler capacity the water passing through the boiler will take a while before it is hot , my old granny had a Greenstar combi boiler 6 feet from the kitchen sink and water pressure that could cut through stone , if she turned the tap on full it took ages before the water went hot but if she let the water dribble out the tap just enough to turn the boiler on then it only took a few seconds to heat and once it was hot you could turn the tap on more..

That prompted me to do a quick calculation - I make it closer to 1.25 litres for that notional 7 metres of pipe. I just adjourned to the kitchen and did the washing up. measuring the hot water flow rate while I was at it. At the much reduced flow that I now have, it took 1 m 25 s to get 13 litres of water into the sink. That suggests that it would take about 8 seconds for the water from the boiler to reach the tap if my pipes are about 7 metres long. (They probably are something like that length.) That is my way of saying that it seems that you are right!

So, preheat would make sure that there is hot water waiting to be delivered to the bathroom about 3 seconds later or to the kitchen about 8 seconds later. That doesn't take into account the fact that the pipes between the boiler and the taps will be cold unless the tap had been run not long ago, so the first lot of hot water would have to warm the pipes on the way. That suggests that for busy households it would be worthwhile lagging the hot water pipes to keep them warm longer between uses. In my case as a sad singleton, it might not be because it could be hours between me using hot water one time and the next. I'm not ripping the floors up to do it, but if the bathroom floor is taken up to install the towel rail/radiator then I will lag the pipes (and secure them better) before the floor is put back down.

It wouldn't. The CH circuit is completely separate from the hot water one and the mains cold feed. The only time the CH circuit is connected to mains pressure water is when the CH is initially pressurised. That's just a temporary commissioning operation.

That is what I thought, and why I have been so baffled.

Perhaps there is fault with the valve in the boiler which sometimes stops it closing reliably?

The problem hasn't manifested itself so far today, having tweaked the stop-cock again last night. No doubt it will happen about 10 seconds after I make this post!

 

[Mr Celine]

[QUOTE 4056187, member: 9609"]Another question for any plumbers out there - how do I know if there is an inhibitor in the system ? I bled a radiator the other day and the water was clear, I had expected it to be very dirty blackish colour.[/QUOTE]

Drain some of the water into a small clean glass jar, filled to the top. Add a clean, non-galvanised steel nail or screw and put a lid on the jar. Put another identical nail or screw into another jar filled with tap water. Leave overnight. If both nails are equally rusty you need to add inhibitor.

 

[ColinJ]

Apologies for half-taking over the thread. I skim-read the first bit and thought that the original question was finished with!

 

[berty bassett]

back to the first question - could it not be the diaphram that is split ? - things would be ok until the water was heated then the valve would dump pressured water - just the thought - i'll go now shall i btw - if theres any chance that it sounded like i knew what i was on about - don't be fooled ! but it can happen

 

[Levo-Lon]

[QUOTE 4057717, member: 9609"]This seems to be dismissed as simply draining some off would entrain enough air / oxygen into the water to promote rust. I might give it a go none the less

I think I may just bite the bullet and buy some inhibitor, drain the system down and refill.[/QUOTE]

no need to drain down..
i just add it via the boiler or a rad..
for rad just shut both valves and drain off enough to allow inhibitor to be added.
boiler requires shutting of flo and return and drain with PRV..tho this can lead to prv failing...which brings ue full circle to pressure loss so use the rad method

 

[subaqua]

I hate combi boilers. Give me a nice big cylinder of hot water any day.

Anyway my DIY solar panel wouldn't work with a combi as it needs to store the solar heated water.

You can have storage with a combi . On an existing system Tee into the heating circuit, fit a 2 port valve cylinder stat to control that pipe the output from cylinder through combi cold feed and keep the water stat low then it will not "super heat " the water. You can then have stored free hot water from solar, with option of extra hot if you need it .

 

[subaqua]

It wouldn't. The CH circuit is completely separate from the hot water one and the mains cold feed. The only time the CH circuit is connected to mains pressure water is when the CH is initially pressurised. That's just a temporary commissioning operation.

Well you would like to think so, but I have seen so many with the isolating valve open a smidge. Methinks there is a leak somewhere and that keeps pressure up in system, but so many are like that.

My loop stays in place as it's a pig to put back on each time but both isolation valves are firmly shut. The one with the thumb turn handle and the ballofix with screwdriver slot. Also have double check valves . Probably breaks WRAS rules or a water byelaw on air breaks.

 

[subaqua]

Doubled flipping post.

Forums bust again !

 

[tony111]

Water hammer in a heating system can be caused by thermostatic radiator valves being installed incorrectly. Look for an arrow on the valve which shows which way the water should flow. If the arrow shows that water should flow into the radiator, then feel the pipe, it should be warmer than the pipe at the other side of the rad. If the arrow Indicates water flowing out of the rad, then that pipe should be cooler than the opposite one. If the valve has an arrow showing both directions, ignore my comments as these can be fitted in any direction.