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Help - underfloor heating not working properly


Headscratcher

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I have had a wet system installed in my house. 5 port manifold with IBO pump and blending valve. 2 port valve installed to allow the UFH to run on it's own circulate with one radiator linked to it to deal with excess boiler heat. I have a combi boiler.

Problem is: when the thermostat calls for heat everything is initially fine.. 2 port valve opens, UFH pump kicks in and heat flows from boiler through blender valve... all going well  after about 2 mins, the flow metres start to show no flow and the temperature in the manifold drops, with no hot water being mixed. 

If I then reduce the temperature to 30 degrees on blender valve, the water temperature ramps up in the manifold and I can then gradually reset it to 45 degrees and all is okay. Without this self adjustment the water in the UFH stays at around 20.

 

Thoughts?

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Just now, Headscratcher said:

Problem is: when the thermostat calls for heat everything is initially fine.. 2 port valve opens, UFH pump kicks in and heat flows from boiler through blender valve... all going well  after about 2 mins, the flow metres start to show no flow and the temperature in the manifold drops, with no hot water being mixed. 

 

Does the ufh loop pump stop or does it keep running when the fault occurs?

Edited by Temp
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That is exactly the same manifold as I have (mine came from someone on ebay)

 

So on the blending valve, the pipe coming in from the bottom is the flow and the pipe exiting to the left is the return.

 

I changed my IBO pumps for WILO (because the IBO ones were far too noisy) so I don't have one to hand for a direct comparison, but the flow of the pump (it has an arrow on the body) should be upwards.

 

I don't think it is a blending valve issue as even if the valve is not asking for any heat, it should just recirculate, so I wonder if you have the pump the wrong way up?

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+1 to check the pump direction. I looked at the manual but it's not clear. The drawing that shows the permitted installation orientation suggests it might be installed pumping downwards by mistake. However if that was the case I don't think the flow meters would work?

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44 minutes ago, ProDave said:

That is exactly the same manifold as I have (mine came from someone on ebay)

 

So on the blending valve, the pipe coming in from the bottom is the flow and the pipe exiting to the left is the return.

 

I changed my IBO pumps for WILO (because the IBO ones were far too noisy) so I don't have one to hand for a direct comparison, but the flow of the pump (it has an arrow on the body) should be upwards.

 

I don't think it is a blending valve issue as even if the valve is not asking for any heat, it should just recirculate, so I wonder if you have the pump the wrong way up?

Spot on. I have just removed the mixing valve and the pump to learn that the plumber installed the boiler flow into the boiler return... so annoyed. I have been battling with this issue for ages and was assured on numerous times it had been done correctly. The indicators are on the bottom of the valve so without removing it, t’was hard to see.

 

thanks for your help. I now somehow have to reconfigure  the pipes which is going to look super untidy.

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5 minutes ago, Temp said:

+1 to check the pump direction. I looked at the manual but it's not clear. The drawing that shows the permitted installation orientation suggests it might be installed pumping downwards by mistake. However if that was the case I don't think the flow meters would work?

Thanks. Found the issue. Flow and return piped incorrectly on mixer... see my response to ProDave.

 

thanks for your help Team DIY. 

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