Unvented on the end of heating circuit

mutley racers · Dec 13, 2018

Hi all. Has anyone come across this before where an unvented cylinder has been put on the end of a radiator circuit of a combi with a zone valve and cylinder stat?

Welder · Dec 13, 2018

Yes. In a very expensive house 'designed' by a, so called, qualified architect who built sheds for Tesco... It was mostly DIY and utter rubbish.
It continues to 'work' because I rewired so the UVC had its own timer and I altered timings so that water was heated only when there was no heating demand. The UVC feeds bathrooms & the combi feeds the kitchen and cloakroom.

mutley racers · Dec 13, 2018

YorkshireDave said:
Yes. In a very expensive house 'designed' by a, so called, qualified architect who built sheds for Tesco... It was mostly DIY and utter rubbish.
It continues to 'work' because I rewired so the UVC had its own timer and I altered timings so that water was heated only when there was no heating demand. The UVC feeds bathrooms & the combi feeds the kitchen and cloakroom.

Hi, so how did you stop the radiators heating up without another zone valve?

This one has a Emmersion heater programmer which is knackered. They had no hot water in the summer so I told them this but apparently they never used it and it was heated by the boiler. The boiler heating was set to off plus the zone valve was knackered. So I replaced the zone valve and turned all rads to off and now they have had hot water for a couple of months.

Now winter has kicked in, all the heat is going to the rads and not the cylinder and so no hot water this morning.

Welder · Dec 13, 2018

Bu66er. I mis-read what you wrote. No this one had a seperate cct for rads but the HW took forever as the htg robbed it.

You can do nothing with that as it stands aside from perhaps running a seperate flow to it or reinstating the immersion.

TBH they will save serious money over time by running a seperate flow no matter what its size. Electricery is somethng like 5 times the cost of gas per KW if I remember correctly and also they'd have teh backup of an immersion should it be reqd.

Personally that's how I'd explain the need to change it to give em a proper home.

Chuck · Dec 13, 2018

mutley racers said:
Hi all. Has anyone come across this before where an unvented cylinder has been put on the end of a radiator circuit of a combi with a zone valve and cylinder stat?

This is pretty much the worst arrangement I can think of. Have you looked at its paperwork? My money says that it was installed by an amateur...

My explanation would be along the lines that unvented cylinders require a lot of power from the boiler when they are reheating. They also need the flow temperature to be as high as possible. These requirements together mean that they have be on their own zone and benefit from being as close to the boiler as possible. Your current system is the opposite of what's best.

Welder · Dec 13, 2018

Chuck said:
This is pretty much the worst arrangement I can think of. Have you looked at its paperwork? My money says that it was installed by an amateur...

My explanation would be along the lines that unvented cylinders require a lot of power from the boiler when they are reheating. They also need the flow temperature to be as high as possible. These requirements together mean that they have be on their own zone and benefit from being as close to the boiler as possible. Your current system is the opposite of what's best.

You are of course correct. I was simply proposing a pragmatic alternative standing more chance of delivering an imperfect but workable soltion rather than the ideal - a complete redesign.

mutley racers · Dec 13, 2018

Chuck said:
This is pretty much the worst arrangement I can think of. Have you looked at its paperwork? My money says that it was installed by an amateur...

My explanation would be along the lines that unvented cylinders require a lot of power from the boiler when they are reheating. They also need the flow temperature to be as high as possible. These requirements together mean that they have be on their own zone and benefit from being as close to the boiler as possible. Your current system is the opposite of what's best.

This is what I have told him. He has said it was all working fine until I serviced his boiler. In June. A month later I get a call saying he has no hot water and that it has gradually diminished since me being there. I go there and discover the zone valve is knackered and the immersion programmer and tell him this design is a bodge. He says he wants a cheap fix for now and so I put a new zone head on.

So a call this morning saying he cannot keep on having issues with his system and paying me to come out to temp repair it.

Chuck · Dec 13, 2018

mutley racers said:
He has said it was all working fine until I serviced his boiler. In June. A month later I get a call saying he has no hot water and that it has gradually diminished since me being there. I go there and discover the zone valve is knackered and the immersion programmer and tell him this design is a bodge. He says he wants a cheap fix for now and so I put a new zone head on.

So a call this morning saying he cannot keep on having issues with his system and paying me to come out to temp repair it.

One possible explanation for this history, is that until the summer they were actually using electricity to heat their water. In June you fixed/changed things so that the boiler was being used instead. This worked, just about, until now when the weather's colder and the radiators are drawing power from the shared zone.

Make sure you really understand the details of the current system before making modifications. Any modification short of separate zone with independent flow and return piped back to the boiler is going to risk reverse flow problems. I.e. it'll be okay in this winter but the customer will call you in the summer saying that their radiators get hot whenever the hot water is on.

mutley racers · Dec 13, 2018

Chuck said:
One possible explanation for this history, is that until the summer they were actually using electricity to heat their water. In June you fixed/changed things so that the boiler was being used instead. This worked, just about, until now when the weather's colder and the radiators are drawing power from the shared zone.

Make sure you really understand the details of the current system before making modifications. Any modification short of separate zone with independent flow and return piped back to the boiler is going to risk reverse flow problems. I.e. it'll be okay in this winter but the customer will call you in the summer saying that their radiators get hot whenever the hot water is on.

This is what I told them. The radiators were getting hot in the summer so all the trv's were turned off and so all the flow just going to the cylinder as well as the immersion heater being on. I told him at the time to just by a new immersion programmer and wack this on the existing back plate so he has the set up he had. Obviously he hasn't changed it.

Chuck · Dec 13, 2018

mutley racers said:
This is what I told them.

They seem to be in good hands. I hope they have the sense to listen to you. Unfortunately, some people seem to think that if they make enough fuss the laws of physics won't apply to them...

Best · Dec 13, 2018

Sounds like it might need a flow and return pipe run entire distance to solely heat the unvented unit, so to avoid any other issues with rads

AWheating · Dec 13, 2018

tell him to flek off, you dont want customers like that.

Welder · Dec 14, 2018

AWheating said:
tell him to flek off, you dont want customers like that.

Why decend to that level? We are better than that so, imho, by demonstrating the moral & tech high ground we become true professionals

Unvented on the end of heating circuit

mutley racers

Welder

mutley racers

Welder

Chuck

Welder

mutley racers

Chuck

mutley racers

Chuck

Best

AWheating

Welder

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