I have a Myson Apollo boiler and a conventional heating and Hotwater
I have recently replaced the pump (myson 53) with a new one
(circulation pumps 53)after it failed but now have the following
When the system is running a small amount of water is coming out of
the overflow from the small black plastic tank in the loft. I was told
the pump may be set too low so I increased it to the second setting
but this only increased the flow of water so I put it back.
I have had it suggested that the thermostats in the boiler might have
gone and was wondering if anybody could tell me which. I understand
there is one for the return water temperature one for high and one for
I am assuming it will be the return as the problem is still there
wether the boiler is set to high or low.
If anybody could clear this up for me or has another suggestion then I
would be grateful for any information.
Slowing it down should reduce the flow. However, you might not be able to do
so if it is already on the slowest setting, or a slower setting doesn't get
everything hot enough. It probably happened when you changed the pump as it
was marginal before, but the new pump is just a little more powerful, enough
to pump over.
Quite frankly, systems with loft tanks are a complete pain in the arse. You
could fiddle around for years with air separators, moving pipework,
adjusting valves and pumps etc. Or you could rip it out and replace with a
proper sealed pressurised system that simply doesn't have all these
problems. There are other advantages too. It is much easier to bleed
radiators and flush the system. You get more storage space in the loft.
Leaks are less likely, as you can remove pipes from the freezing loft space.
Any leaks you do get are much less serious, as there is a limit to the
amount of water lost due to the manual fill arrangements.
To make the change, you just need a kit to upgrade, which will include a
pressure vessel, pressure relief valve, filling loop and pressure gauge. You
install these items, rip out the tank and you're done. It is a relatively
simple DIY plumbing job, similar in scope to plumbing in some new taps.
You would need to ensure that your existing system is compatible with sealed
operation. This basically means your boiler must have a safety cutout.
(in case of wraps:)
The exact size you need depends on the size of your system. They have kits
from 8 litres to 24 litres. If you know the number and average size of the
radiators, you can calculate the minimum size required. Using one that is
too big isn't a problem. They vary from 40 to 50 quid including VAT
depending on size.
While agreeing that if you actually need the space taken up by the header
tank a sealed system may make sense, header tanks worked perfectly well
for many years before them. Sometimes the simple way is actually the best.
*A journey of a thousand sites begins with a single click *
Dave Plowman email@example.com London SW 12
I see absolutely no advantages to open systems than these marginal ones:
1. Your boiler might require it.
2. You already have one and don't want to spend 50 quid upgrading.
3. Certain heat bank applications with common circulating water.
The advantages list goes on and on. Header tank systems rarely work well or
predictably, which is why sealed operation is now the norm.
Only 50 quid? And how about the reliability of pressure vessels?
I reckon you're much exaggerating the problems with header tanks. And I'd
say sealed systems are popular for the same reasons as combis - they are
easier to install so make a larger profit for the plumber.
*Sorry, I don't date outside my species.
Dave Plowman firstname.lastname@example.org London SW 12
That's the parts cost, provided you DIY. I reckon it would take me about 2
hours of my time in addition to affix a sealed system kit and cap off the
old pipes. This includes drilling a hole through the wall for the pressure
relief. The kit simply requires you to insert a T at convenient points in
the CH circuit and rising main and attach using compression joints.
I have a house with header-tank style oil fired CH which has worked for
years perfectly fine. We now wish to install 3 new rads in the attic where
the header tank is. This was going to involve moving the header tank from
its present location almost at floor level up the wall to create enough head
to stop pump-over and allow the new rads (300mm installed low as poss) to
Had never heard about sealed pressure system you mention. Would there be any
problems with fitting such a kit to my system to avoid the bother of moving
the header tank like bursting rads or creating leaks where there didnt used
to be any...??
There is room in the boiler cupboard, just, probably to install a pressure
vessel and there is an outside wall to pop the vent through. What safety
cut out does the boiler require? (already has adjustable thermostat as per
Could the pressure vessel be installed in the place of the header tank in
the attic or does it have to be nr the boiler?
I would VERY strongly recommend switching to sealed operation. For loft
conversions, it is a no-brainer decision, provided your boiler has the
required safety cutouts.
Sometimes, you do get leaks that weren't there before. However, if you do,
then it usually indicates that the joint/pipework was on its last legs
anyway, so you can be thankful for the warning. Occasionally some radiator
unions may need a slight nipping up, but this is rare. If your pipework
really can't take 1.5bar, then it is shot. Period.
Yes. It is a popular location for it, as it already has a mains pressure
cold water feed, an overflow pipe which can be replaced by a copper pressure
relief one, and a connection into the system. The main objection is normally
that it is in a loft, where the pressure gauge and refill point are
inaccessible. In a loft conversion, this is no longer the case.
When installing, it is advisable to add an additive filling point too, so
you can use cheap unconcentrated treatment chemicals. This is simply a short
vertical spur of pipe with an isolating valve in it. You pour the chemicals
into a funnel at the top before refilling with water.
It just needs a second device to cut the gas if the system starts boiling.
This is often a non-adjustable 90-95C manually resetable thermostat next to
the main thermostat. If you state the make and model of your boiler, someone
here might know if it is already so equiped.
Fairly sure there isnt any additive in the system at the moment... The only
slight complication is that as well as the CH heating the hot water
cylinder- an Aga also does so via thermo-syphon. Am not quite sure how both
heat sources are plumbed into the cylinder coil, will investigate...
The system works with two motorised gate valves, as opposed to a mid port
valve if this makes any difference...?
In that case, no there isnt a 95 C cut out- surely easy to fit as a clamp on
pipe arranghement with normally closed contacts..?
Thanks muchly for the info so far
This can get complicated, unless the Aga has its own coil in the cylinder
and doesn't share water with the boiler. If it does share water, you're
getting into Dunsley Neutraliser territory. I don't know if you can run one
of these (or an Aga/Rayburn) with a sealed system. I can't think of a
technical reason why not, but you'd definitely have to check and could well
be disappointed. Perhaps someone here already knows.
There are other alternatives, depending on how satisfied you are with your
system and how deep your pockets are. You could, for example, replace the
cylinder with an indirect heat bank. (DPS would be the specialists in this
field). Then, the CH circuit would be conventional indirect through the coil
(i.e. Y-Plan/S-Plan). The Aga circuit could remain gravity circulated (or
pump assisted) using gravity fed water shared with the heat bank. This would
have the advantage of providing oodles of mains pressure hot water to the
taps, providing superlative multiple shower performance and good bath
performance, assuming your water supply is good. If not, you can still use a
header tank (possibly pumped) for the cold water supply, you just don't get
the advantages of mains water.
Optionally, you can also run the radiators from the heat bank too. Although
not strictly necessary, this would enable the Aga to power the radiators,
too. It also provides the opportunity through twin thermostat/high
hysterysis controls to allow efficient 100% burns from the oil boiler and
gives better performance when little heating is required, as the boiler
won't drop off the bottom of its modulating range and cycle frequently. (It
will cycle using 100% burn over a long period with varying mark/space ratio,
which is much more efficient than cycling over a 2 minute period at minimum
The main disadvantage is that it is difficult to take advantage of
condensing operation very easily (if you have a condensing boiler). However,
it will condense under many conditions and will definitely take advantage of
the greater heat exchanger efficiency. The gains from the anti cylcing
nature of the system will probably outweigh the disadvantages of the higher
flow temperatures, although mileage may vary.
Increasing the pump rate would likely make the problem worse.
One explanation might be a blockage in the system, cause by sludge, or radiator
valves (including lockshields) and zone valves not opening enough.
Rasing the maximum height of the overflow pipe might well be a way of solving
the problem, so that the vertical distance between the highest point of the
overflow pipe and the level of the water in the tank is increased.
First of all do you mean the overflow (which carries water away from the
tank to an open pipe discharging somewhere outside the house where it
is|should be visible?
Or do you mean the vent pipe which is roughly like the crook of a walking
stick and opens over the tank itself?
From the sysmptoms you describe it sounds to me (and everyone else who's
replied to this thread) like the latter. If it is then apart from making
sure the top of the walking-stick section is as high as possible above the
tank and the water level in the tank when cold is only about 2-3", you
should check that the outlet (feed) pipe from the tank and the vent pipe
both join the main pipework close together - less than 6" apart.
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