adam email@example.com (Adam) wrote in message
I know it's bad form to follow up one's own posting, but more info...
The knocking occurred at least twice last night - once around 1130,
once around 0230. The hot water was turned off at the wall thermostat
for the boiler.
There is, however, a switch in the hall near the boiler that says 'hot
water' or similar with a red light embedded below the switch itself.
Switching this off caused the knocking to tail away. Switching it
back on caused the knocking to return after a few minutes. Now, that
sounds like an electric element heating water to a boil to me...
Have we got electrically heated water in addition to the gas boiler?
When we first moved in and switched the water on (at the boiler
thermostat), we were expecting nearly instantaneous water because we
believed we had a combi, but there was no hot water until we switched
this 'hot water' circuit on (and then we had to wait a half hour or
so). Has this been installed in the past because someone couldn't get
the boiler to heat water? Most importantly, can I find out what in
installed in my house without paying a fortune to get a plumber in to
suck his teeth and tell me I need to spend a fortune on replacing it
I forgot to bring the manual for the boiler into identify it - it is a
Vokera, though. I'll try to remember to do that tomorrow...
Any advice gratefully received...
Confused - Adam...
It would have been installed anyway as part of the original installation, if
nothing else as a backup. Accepting that...
If you didn't get any hot water until you turned on the electric heater,
possibly, or maybe the boiler was never designed/installed to.
Find out exactly what stuff is there and post again here. Follow pipes,
especially around the boiler and the tank. Find out *exactly* how many pipes
enter the hot water tank and where. If, for example, there is one pipe out
the top and one pipe in the bottom, then the only water heating you have is
As you are getting boiling, the the thermostat for the tank may be faulty.
This is a relatively simple DIY task to change but involves electrical
connections. If you feel you are not competent, get someone who is. It will
be found under a cylindrical metal cap on the cylinder somewhere (isolate
before taking the cap off). The thermostat will slide out separately and cna
be replaced (with one of the same length). There is clearly nothing wrong
with the element itself!
1. Your only water heating is electrical by design - expensive to run,
expensive to change (but, bar the thermostat possibly, it is working!)
2. The water heating part of the heating circuit driven by the boiler (if it
exists) is not operational. Shouldn't be too expensive to fix.
(anti-spam is as easy as 1-2-3 - not)
Thanks Bob, I will. I didn't get a chance to do anything last night,
but I will try to take a few minutes noting everything and posting it
Excellent, I'll give that a try. Is it possible that it is simply a
matter of adjusting the thermostat, or are these set at a fixed
(presumably just below boiling) level?
Also worth noting is that last night, when I drew a bath, the hot
water was plenty hot enough, but definitely not scalding. I can try
to get hold of a thermometer to measure the temperature at the tap...
Thanks for the advice - I'll post the info as soon as I get a chance.
Cheers - Adam...
First of all, thanks Bob for all the excellent information. I did
some investigating last night, and...
[This is long, and my description are probably a bit cr&p...]
-8<- for brevity ->8-
that was my first thought, but then I understand that Edinburgh is a
particularly soft water area, and I understnad that the cylinder is
only around 3 years old, it having been installed when the loft
conversion was done.
Excellent, thanks - I couldn't see that last night (the cylinder is
accessed through a small cupboard door), but now I know where and what
I'm looking for.
-8<- snip elictrical connection details ->8-
Will try this.
Well, following my investigations of pipe routing last night, I
believe I hve worked out what's going on. I'll try to describe it as
best I can, but it's a bit of a jumble...
The boiler is a Vokera Mynute 20SE and is not, as I had been told by
the previous owner, a combi. It does, however, have the ability to
run a hot water cylinder using either a 'Y' or 'S' configuration (I
don't entirely understand these terms, but I think I have a rough idea
from the manual' layout diagrams); from the piping layout it appears
that our boiler is heating water using the 'S' configuration - at
least, there are two motorised valves in the cupboard - with the
downstairs hall radiator as the bypass. I assume from the layout
diagram in the boiler manual that this means the boiler can heat the
radiators or the hot water cylinder independantly.
There are just three pipes leading to the boiler - I assume these are
the inflow, outflow and gas.
There appear to be three pipes leading to the cylinder, although I
presume there's one more I can't see - I assume these are the mains
input, hot water output and boiler system inflow/outflow.
The pipes adjacent to the hot water cylinder appear to originate from
the boiler (at least, two disappear under the floor, roughly towards
the boiler, and were warm when I was working last night. One (I
assume boiler outflow) appears to feed the cylinder via one motorised
valve, has a pipe leading off (I assume) to the bypass and feeds what
appears to be the rest of the heating system via the other valve; it
is also connected to the mains water via a flexible hose. The other
(I assume the boiler inflow) appears to feed the cylinder and the two
heating pipes. Of course, they also appear to be connected in random
ways to each other, but the heating works, so I'll ignore that!
There were two hand taps in the cupboard: one is on what I assume is
the boiler inflow pipe, just next to where it exits the hot water
cylinder; the other was on the boiler outflow pipe, above the joint
that leads to the T-joint to which both motor valves are attached.
Opening each of these about a half turn appears to have given us hot
water this morning despite the 'hot water' switch (electrical
immersion heater) being turned off.
So I assume the electric immersion heater is a backup system to the
boiler, which now *appears* to be working.
-8<- snip details of replacing immersion heater and/or hot water
I hope replacement won't be necessary, at least for the moment. Will
the kettling cause lots of damage, or is it mostly just an auditory
Thanks again for all the helpful advice - Adam...
It sounds as though you have now analysed the system, at least. A few
Your presumption on the pipes to the cylinder is probably correct - it is
likely the cold feed to the cylinder (from a header tank in the loft/on top
of the cylinder/somewhere else above it) is round the back somewhere. The
pipe that comes out the top of the cylinder is the DHW (domestic hot water)
take off, where the water for the hot taps comes out. The heating pipes
from/to the boiler normally come in and out the side, one above the other
(inside they are connected by a copper coiled pipe which keeps the DHW and
the boiler water seperate but allows heat exchange).
There should be a thermostat on the cylinder between, vertically speaking,
the boiler pipes. This will open the motorised valve and request heat from
the boiler (if the water switch is ON) when the water temperature drops.
There must be a heating/water control panel somewhere (behind a cover in the
boiler or on a wall somewhere).
The big question is "why was the water circuit valved off?". I fear I can't
imagine anyone doing this unless there was a problem! One likely problem (if
there is one) is a leak between the heating coil in the cylinder and the
DHW. If you run the system as it is intended, and there is a leak,
eventually the DHW cold header tank will overflow (the pump pressure forces
water from the boiler circuit into the DHW and "backfills" it). An
unscrupulous seller might have just valved off the tank and switched to
electric heating and not said anything. OTOH they may just have been stupid
and not realised it was valved off! I hope it's the latter.
The kettling will just be an auditory annoyance but it may still be worth
checking the immersion heater thermostat.
You are, at least, at the stage where you can experiment and found out how
the system operates and if necessary repair it rather than be faced with a
(anti-spam is as easy as 1-2-3 - not)
There are some 'boxes' with electrical feeds strapped to the side of
the cylinder with what looks like the wire cord used to hold up net
curtains. One of these has a dial on it, and from your description
I'm willing to bet (a small, nominal amount!) that that is the
thermostat. There doesn't appear to be any 'kettling' whan the boiler
(rather than the electrical system) is running the DHW.
Control panel - do you mean the dual hot water and central heating
timer panel that's in the kitchen downstairs?
It wasn't actually turned off - it was open, but only just. All I've
done is open it by a further half-turn or so. I take your point,
however, about possible causes for that, and I'll chek the area for
leaks as soon as I get home.
WRT to DHW header tank - presumably this would have to be physically
sited higher than the top of the DHW cylinder? Is it possible the
cylinder is fed at mains pressure? I ask because there is only one
header tank in the loft area (that I have found) and that is level
with the cylinder (the bottom of the tank is level with the bottom of
the cylinder - I guess the top of the water level would be about level
with the upper boiler pipe). I suppose I can check to see if this
fills the tank by seeing if the ball-valve opens when a hot tap is
Aye, will do as soon as I get home. As I said before, at least I know
what I'm loking for now...
-8<- snippety-do-dah ->8-
Heh, thanks - I sincerely hope I don't need it! Actually, I'm
starting to enjoy this - it's amazing how quickly you start to
understand things once you get over the fear...
Cheers - Adam...
Sorry ignore my other reply - hit SEND by mistake!...
Yes. There will never be kettling from the boiler fed system as the heat
source is always well below boiling point - not the case with an electric
element, where, if there's obstruction to free flow of water over it,
localised temperatures can exceed 100C.
Yes you could do that. Try turning on the cold tap in the kitchen and trying
to stop the flow by putting your thumb over the end - this will give a feel
for the incoming mains hydrostatic pressure. Then do the same with the hot
tap. If it requires much less effort to stop the flow, it must be run from a
header tank, not the mains. If it's about the same, it will be a mains
pressurised system. Some vented cylinders ("Fortic" et al) have the header
tank integral as the top part of the cylinder. The other tank sounds like
the header tank for the boiler circuit (which needs its own).
(anti-spam is as easy as 1-2-3 - not)
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