We have just had a new worcester bosch system boiler fitted to a fully pumped system. In the night we heard lots of noise from all the pipework and the radiators so i went in the loft today to check something and found the header tank which tops up the system has quite hot water in it !!
is this normal? i suspect not
what could this be caused by?
apart from the noise which only seems to happen at night, everything seems ok
cheers
Daz
ps. it has just been converted to a standard Y plan system because we had no independant control over the hot water so they added a 3-way valve
i have just watched the system and noted as soon as the demand for the heating goes off , the pump seems to flow all the hot water into the header tank in the loft for about 5-10 seconds. The tank then seems to go back to its correct level.
mine has definately got a header tank. The valve is a honeywell 3 position diverter valve. The tank has a built in header tank that supplies cold water to be heated up and the other header is in the loft which tops up the sealed heated water that flows through the coil in the tank unless i have it totally wrong.
Your primary circulation system is either vented or unvented (sealed).
If unvented, there is no header tank - by definition - but there is a pressure vessel instead, to allow for expansion, and a filling loop to allow the system to be initially filled with water.
If vented, there is a fill & expansion tank - but no pressure vessel or filling loop.
The term 'system boiler' is usually associated with a sealed/pressurised system - which has an expansion vessel - and often a pump also - inside the boiler casing.
So a slightly more detailed description of your system would be helpful.
my system has just been converted by installing a diverter valve to hopefully allow me to select heating OR hotwater. I have had fitted a worcester bosch condensing (non combi hence system) boiler. The pump has a tee piece straight after it, one pipe goes to an open pipe just above the water line in a header tank in the loft and the other goes to AB connection on the 3 way valve. It is definately vented , no fill loop or pressure vessels.
A system boiler has a pump and pressure vessel inside, you have a "heating" boiler.
Does the boiler have a pump overrun? If so that is a problem here. Where does the 15mm feed pipe from the F&E tank go to? It is best to have this fill the system just before the tee after the pump, So, boiler flow ->
pump -> tee to F&E tank (feed) -> directly after another tee that goes to the open vent over the F&E tank -> the diverter valve. This will prevent pump over.
The diverter de-energises to either CH or DHW port open. Any pump overrun should go though this port, not over the F&E tank, Having the feed and open vent pipe teed off next to each other put equal pressure on each. The feed tee MUST be nearest the boiler.
AIUI, not being a combi doesn't automatically make it a 'system' boiler - 'conventional' may be a better word.
So there's a vent pipe connected *after* the pump, which loops over the top of the F&E tank. There must also be a feed pipe running from the bottom of the F&E tank. Where does that connect into the boiler flow pipework?
You have pretty certainly got a case of pump-over - where water is being pumped up the vent pipe into the F&E tank - to be replaced by water flowing down the fill pipe, and back into the system. This is *bad*. Not only is it wasting heat, it is also introducing trapped air into the system - which will cause corrosion.
If your pump has several speeds, you could try slowing it down a bit - to see whether that cures the pump-over whilst still heating the radiators adequately. Otherwise, some plumbing mods will be needed. The fill and vent pipe connections into the main flow pipe should both be on the boiler side of the pump rather than after the pump, and they should be no more than 100 mm apart - so that they both experience essentially the same dynamic pressure - making it impossible for water to circulate between them.
I have mis informed u all. The overflow to the header IS before the pump i.e on the suction side of the pump. The pump has a red dial on the electrical box numbered 1 to 3. I take it this is the speed. It is set to 2 at the moment. Would it be o.k to lower to
It can be quite normal. The header tank is in fact a feed and expansion tank. So not only does it feed water into the system when required, it also exists to allow the water in the system somewhere to expand as it heats up. Hence when operating you would expect the content of the tank to be at least worm.
see above, and also in your case "pumping over".
Does you pump have a speed selection switch on it? If so what speed is it running at? If not already the slowest speed have you tried lowering it?
just an update, the corgi registered installers came back around today and fitted an automatic bypass, the problem seems to be the same but now the boilers main indicator light flashes on/off as the boiler shuts down. In the manual it says its due to overheating which i suppose is the hot water coming straight back from the pump via the bypass. The problems only seem to happen at night.........which inturn wakes everyone up with the noise of the water pumping over. I am using the honeywell cm-zone trvs and controller if anyone has any experience of setting these up i could do with some advice !
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