Hi All,
I'm hoping for some assistance here. We've recently had a Vaillant 837, rads and a UFH system installed as part of a refurb. The majority of the house is served by rads with an extension that has a single zone room pack from John Guest. Its been setup with 2 x zone valves so both the rads and the UFH have their own programmable room stats. The operation of the control side is fine with both being able to fire up the boiler as expected.
The issue arises when the UFH is on alone. The boiler fires up and very quickly goes into anti-cycling mode. I see the tempertaure display on the boiler rise rapidly when it fires up for up to 15 seconds and then it cuts out to anti-cycling when it hits around 60 degs C. I've altered d.0 to 12 (it was at factory default 28) and this has slowed down the time before it goes into anti-cycling but hasn't solved the problem. I also reduced the anti-cycling max time to 5 mins to see if that helped but it didn't.
My theory is that the UFH is not taking enough flow from the boiler (as the manifold mixes the UFH return cooler water with the incoming hot from the boiler to get the right temperature flowing into the UFH). If the return from the UFH is warm, then it seems to take very little from the boiler. I'm assuming here that the boiler internal bypass is firing which flows the hot straight back around and makes the boiler go into anti-cycling mode.
When in anti-cycling mode, the water temperature drops well below what the UFH is asking for and the floor cools down. The floor doesn't really get up to temp when this occurs.
Has anyone got any guidance on what I should check/investigate here or any other theories on what I can do to fix it. Is my setup correct or do I need something special to connect a boiler like this to the UFH?
I've currently got the zone valve for the rads set to manual so it is always open which allows 'excess' heated water to flow through the rads which don't have TRVs on them (1 x hallway and 2 x bathroom towel rails) which seems to stop the anti-cycling.
Also, as a QQ on the side, what temp should i have the UFH set at ? Its a 75mm screeded floor with stone tiles on top.
TIA
DM
I'm hoping for some assistance here. We've recently had a Vaillant 837, rads and a UFH system installed as part of a refurb. The majority of the house is served by rads with an extension that has a single zone room pack from John Guest. Its been setup with 2 x zone valves so both the rads and the UFH have their own programmable room stats. The operation of the control side is fine with both being able to fire up the boiler as expected.
The issue arises when the UFH is on alone. The boiler fires up and very quickly goes into anti-cycling mode. I see the tempertaure display on the boiler rise rapidly when it fires up for up to 15 seconds and then it cuts out to anti-cycling when it hits around 60 degs C. I've altered d.0 to 12 (it was at factory default 28) and this has slowed down the time before it goes into anti-cycling but hasn't solved the problem. I also reduced the anti-cycling max time to 5 mins to see if that helped but it didn't.
My theory is that the UFH is not taking enough flow from the boiler (as the manifold mixes the UFH return cooler water with the incoming hot from the boiler to get the right temperature flowing into the UFH). If the return from the UFH is warm, then it seems to take very little from the boiler. I'm assuming here that the boiler internal bypass is firing which flows the hot straight back around and makes the boiler go into anti-cycling mode.
When in anti-cycling mode, the water temperature drops well below what the UFH is asking for and the floor cools down. The floor doesn't really get up to temp when this occurs.
Has anyone got any guidance on what I should check/investigate here or any other theories on what I can do to fix it. Is my setup correct or do I need something special to connect a boiler like this to the UFH?
I've currently got the zone valve for the rads set to manual so it is always open which allows 'excess' heated water to flow through the rads which don't have TRVs on them (1 x hallway and 2 x bathroom towel rails) which seems to stop the anti-cycling.
Also, as a QQ on the side, what temp should i have the UFH set at ? Its a 75mm screeded floor with stone tiles on top.
TIA
DM