Boiler stove pumping over with Laddomat

[ChrisSig]

Hello everyone, I'm looking for some advice on a boiler stove installation which I have recently completed. The part of the system I need help with comprises a boiler stove and thermal store, both on the ground floor, a Laddomat and pipework connecting the two, plus a heat leak radiator gravity circuit on the first floor. Due to constraints in the property, the Laddomat and tank-stove piping are routed in the void between the ground and first floors. The thermal store is open vented to the F&E tank. In order to provide a continuously rising vent to the stove, I have installed a tee on the gravity circuit. The thermal store also has a continuously rising vent to the F&E tank. The feed from the F&E tank is connected to the thermal store, making this the neutral point of the system.

 

My issue is that when the Laddomat pump is running, the system pumps over through the vent on the gravity circuit. I had feared that this might happen due to the pump head, which by design is making the stove and gravity circuit a high pressure point in the system. I can't see a good way to rectify this however:

•  I can relocate the vent on the stove circuit to the pumped flow between the boiler and the tank, however due to the way the pipes have to run because of changing floor levels on the first floor I can't get this very close to the tank. So the pressure in the stove vent pipe will still be quite a bit higher than at the tank. I don't think I have enough headroom in the loft to raise the vent pipe high enough to overcome the static head, though I wouldn't know for sure except by redoing this part of the system;
• I can relocate the vent on the stove circuit to the pumped return before the Laddomat. This will be at a suitably low pressure to avoid pumping over, but I don't think this provides a suitable vent path as this is then routed through the Laddomat pump and valve, which is normally closed except when at temperature
• I can remove the second vent to the boiler stove completely. The system has no possibility of over-pressurising in reality since the stove is hydraulically connected to the vented thermal store with no valves etc via the pumped flow connection, but this vent route is not continuously rising. Initial air removal can still be achieved via bleeding the heat leak radiator. This would be my preferred option, but I don't know if it is regulation compliant (I fear not). I can't find anything in the Building Regulations that explicitly addresses this and as far as I can tell all the relevant guidance is in Hetas and British Standards documents which are not accessible to mere mortals.

 

I have included a crude system diagram to illustrate the current installation. Any guidance gratefully received. I'm sure plenty of pumped stove installations must get around this issue, but I have not found any information on how to achieve this.

 

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