Do I need an expansion vessel?

[fidom]

Not sure if anyone here has dealings with continental water heaters but here goes. I'm from UK but living in Croatia. I have no gas here but plenty of forests so I put in a woodburning central heating system. I used a UK type indirect cylinder for the hot water and the system was pumped CH, gravity DHW. It never worked properly though, the water never got hot and I always needed to use the immersion heater. I discovered the reason for this when the heat exchanger developed a leak in the cylinder and the CH expansion tank overflowed. I took the immersion heater out, shone a light into the cylinder and could see the heat exchanger coil was small bore pipe, not suitable for gravity systems. I could not get a new UK type cylinder here so I bought a secondhand mains pressure indirect cylinder. It is only 1.8kw so not as quick to heat as the UK one but it seemed to be working on electric heat. As it is mains pressure I dispensed with the cold water tank and just connected it to the hot and cold circuits. Water pressure here is not high so I didn't fit a reducing valve. The first night I left it on and at 4 am had a flood, the shower pump had burst. Do these heaters have an integral expansion vessel or should I have fitted an external one? https://netkazan.hu/termek/6663/ari...jYKjDQiX8dID_FGygYwDk4y-E6lEm5fT0h963OElNgQWI

 

[Bodgedbuild]

You REALLY need a qualified plumber with whatever the Croation regulations certify as for working on pressurized systems.
https://www.youtube.com/watch?list=FLZIxVmben2r-sJIu9xJBisQ&v=rGWmONHipVo

 

[Harry Bloomfield]

Water pressure here is not high so I didn't fit a reducing valve. The first night I left it on and at 4 am had a flood, the shower pump had burst. Do these heaters have an integral expansion vessel or should I have fitted an external one? https://netkazan.hu/termek/6663/ari...jYKjDQiX8dID_FGygYwDk4y-E6lEm5fT0h963OElNgQWI

When water turns to steam, the steam occupies 1500x the volume, so what you have there is a very dangerous bomb. You were lucky this time, that the shower pump let go gently - you might not be that lucky next time. For your own safety - Get someone in that is qualified.

 

[bernardgreen]

The water system should also be capable of absorbing or disposing of the heat from the fire if the mains water supply fails. This often requires a store of cold water that can absorb the heat until the fire is shut down

 

[Madrab]

@ 100L, the similar ones in the UK would have come with an unvented safety kit, that would include at least a Temp Pressure Relief Valve an EV and a Pressure Relief Valve.

You really shouldn't be using an uncontrolled energy source to heat any unvented HW cylinder, especially without any safety features fitted.

 

[fidom]

I found a UK supplier of these water heaters and asked the same question. They say the Ariston does include a pressure vessel. It could be that the one in my unit is faulty though.
https://electricaldealsdirect.co.uk/water-heating/ariston-water-heaters.html

 

[lostinthelight]

To use a WB in an unvented system it has to be a special type that has provision to rapidly cool the hot water by mixing with cold. There has been a recent thread on this
Edit: link from that thread, https://www.greymetal.co.uk/install...ting/pressurised-central-heating-systems.html

 

[Madrab]

The closest one that would compare is the PRO1 ECO, that is supplied with a seperate unvented kit. Looking at your original link it doesn't seem like the unit has an internal EV.

Without the MI though it's hard to confirm.