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Discuss Hot water only lasts 2 - 3 minutes before slowly dropping to cold. in the DIY Plumbing Forum area at PlumbersForums.net

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21
Hi all,

Hot water only lasts 2 - 3 minutes, if I turn it off for a minute hot water returns for a couple more minutes. It seems to last longer on a lower pressure. We had a plumber change the heat exchanger which didn’t make a difference. And it’s not the thermal mixer in the shower as we had that changed too. It happens on all hot taps but really only affects us in the shower. The boiler is a 17 year old Valliant Ecomax combi so I’m thinking that it’s probably just time to replace the boiler but would rather not spend that sort of dosh if there is an easy fix. I have also flushed the system twice with sentinel cleaner which might have made a small difference. But our radiators are hot so I’m confused why replacing the heat exchanger didn’t make a difference. As a side note there have been a few days where the ignition flame didn’t come on automatically and we needed to press button to ignite but I wonder it that might be linked in any way.

thanks in advance for any advice.
 
Messages
1,953
I’m confused why replacing the heat exchanger didn’t make a difference.
Heat exchanger would not be my diagnosis for the symptoms you describe. AIUI, we're not allowed to discuss boiler repairs on this forum for 'legal reasons' but a heating engineer should be able to fix the problem without difficulty.

Personaly, I would think twice about spending any money on repairing a 17 year old combi. This is particularly the case if it's a reasonable time to have a replacement installed. But you should discuss the repair / replace decision with your engineer.
 

Ric2013

Plumber
Messages
2,940
I think we can discuss to a point, now this is an international forum?

Which boiler heat exchanger was replaced, out of interest? There are two in a combi boiler so I assume you are referring to one of these. If you don't know, this is a discussion you need to have with the gas installer that repaired the boiler and who, really, should be able to disgnose the fault.
 
Messages
21
I think we can discuss to a point, now this is an international forum?

Which boiler heat exchanger was replaced, out of interest? There are two in a combi boiler so I assume you are referring to one of these. If you don't know, this is a discussion you need to have with the gas installer that repaired the boiler and who, really, should be able to disgnose the fault.
It was the DHW, from my understanding if it’s the main heat exchanger you might as well replace the whole boiler.
 

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Messages
21
I think we can discuss to a point, now this is an international forum?

Which boiler heat exchanger was replaced, out of interest? There are two in a combi boiler so I assume you are referring to one of these. If you don't know, this is a discussion you need to have with the gas installer that repaired the boiler and who, really, should be able to disgnose the fault.
Heat exchanger would not be my diagnosis for the symptoms you describe. AIUI, we're not allowed to discuss boiler repairs on this forum for 'legal reasons' but a heating engineer should be able to fix the problem without difficulty.

Personaly, I would think twice about spending any money on repairing a 17 year old combi. This is particularly the case if it's a reasonable time to have a replacement installed. But you should discuss the repair / replace decision with your engineer.
Thanks for your reply, we are going to be moving house by the end of the year so I would really rather a quick fix if there is one.
 
Messages
1,634
At that very small flowrate a 25kw boiler will maintain a temp of 65C (from mains at 7C) maybe boiler not modulating and this is the over temp limit and burner is switching off then back in again when the temp falls, open another hot tap to increase the flowrate and see if it still runs hot/cold. Will need RGI one way or the other anyhow except you can see something obvious external to the boiler to cause this very low flow rate which the boiler should still be able to handle by modulation.
 

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