Be sure to empty and fill the system several times once the chemicals have done their work. A simple pressure drop will not evacuate the jungle juice or suspended particles that you do not want in the system. Else the chemical cleanse will be for nought. In fact give sentinel a call and ask them what the procedure is post treatment
Hot water flowing from vent pipe into loft tank
- Thread starter wardr77
- Start date
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The indications would point to a blockage and I suggest you cut the pipework out...I've had so many close coupled feed & vents that you can barely get a pencil through...and the scale can be so solid it would need drilling out.
Sure your chemicals might open out the bore a little to get it working ok again but how long will it last?
The whole point of the feed & vent being so close is to keep them at almost identical pressure.
The pressure at that point (known as the neutral point) is constant regardless of the pump running or not.
On your system when the pump is running its inlet is slightly below the static pressure (the pressure when the pump is not running) since there is only a short lenght of pipe to the neutral point and little pressure drop.
The outlet of the pump will be somewhat higher than the static pressure. The pressure is determined by the system flowrate and friction and will be somewhere on the pumps operating curve.
This higher pressure will gradually fall all the way round the system to the neutral point.
Normally when the water is flowing between the tees from right to left (and because there is virtually zero pressure difference due to the large bore pipework and closeness of the tees) the water will not rise in the vent pipe (or no more than 5 or 10mm above the vessel level).
But introduce a blockage and the pressure drop substantially increases between the tees, the vent connection pressure is no longer close to the neutral point pressure but rises and therefore the water level rises in the vent pipe too and if the loop over the F&E cistern is minimal pumping over with ensue.
You could possibly mask the problem by extending the loop higher as a temporary fix
Tell us what the make & model of boiler it is.
Sure your chemicals might open out the bore a little to get it working ok again but how long will it last?
The whole point of the feed & vent being so close is to keep them at almost identical pressure.
The pressure at that point (known as the neutral point) is constant regardless of the pump running or not.
On your system when the pump is running its inlet is slightly below the static pressure (the pressure when the pump is not running) since there is only a short lenght of pipe to the neutral point and little pressure drop.
The outlet of the pump will be somewhat higher than the static pressure. The pressure is determined by the system flowrate and friction and will be somewhere on the pumps operating curve.
This higher pressure will gradually fall all the way round the system to the neutral point.
Normally when the water is flowing between the tees from right to left (and because there is virtually zero pressure difference due to the large bore pipework and closeness of the tees) the water will not rise in the vent pipe (or no more than 5 or 10mm above the vessel level).
But introduce a blockage and the pressure drop substantially increases between the tees, the vent connection pressure is no longer close to the neutral point pressure but rises and therefore the water level rises in the vent pipe too and if the loop over the F&E cistern is minimal pumping over with ensue.
You could possibly mask the problem by extending the loop higher as a temporary fix
Tell us what the make & model of boiler it is.
You are quite right,Sorry
Hi Thanks for this information, gives good explanation as to why the water finds its way up the vent.
Boiler is a floor mounted Worcester Bosch Greenstar FS 30cdi regular
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