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How to correct imbalance in HW/CH Unvented Indirect system please?

Postby keratos » Mon Jan 25, 2021 9:46 pm

My girlfriend's sister has moved into a newbuild (well 10 yrs old now so not new) home. It has an unvented indirect heating system. The hot water is not getting hot enough.

We have balanced the rads, bled them, and the CH is perfect an cosy. But if the central heating is on at the same time as the hot water, then the water is useless for a bath or shower - it's tepid not HOT hot. If the heating is turned off with hot water on, then the water is warm but not hot.

I checked the two zone valves and they are operating fine. But when she moved in it was fine but her son "played" with the "red wheels" she said. I went round and she pointed to what is the gate valve on the heat exchanger return pipe. So it has been turned but I have no idea how much and in what direction.

So without a flow meter to set this gate valve correctly - or as near as - I could measure the temp drop across the boiler feed to the exchange coil, and the return (on which the gate valve is installed). Is there a "an about estimate" I can use so that when both zone valves are open (HW and CH on) I can take a temp reading of the flow in and out of the exchange and adjust the gate valve accordingly until I get the approx "ok" temp drop across the two ?? I can't think of another way.

She is disabled and on benefits and has contacted a Gas engineer who is quoting £250+VAT , she cannot afford that just after xmas.

Can someone help please and offer advice on the above.


Simply Build It

Postby stoneyboy » Thu Jan 28, 2021 10:02 pm

Hi keratos.
Suggest you close the valve completely and then open it 1 turn. Check if this cures the problem with HW.
Otherwise get the gas man in, get the system set up and remove all handles on valves.
Regards S
Rank: Project Manager
Posts: 5342
Joined: Wed Dec 10, 2008 6:44 pm

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