Main Combi 30HE DHW Problem

[fruitcake]

Hi all,

Hoping someone can give me some advice as to the cause of the issue I am having with my boiler.

Boiler is approx 5 years old and has been pretty reliable but recently I have noticed the hot water is not heating properly. This seems to be getting worse and is now to the point where I can now hold my hand under the hot tap when on fully. However if the heating is on the hot water does seem to heat properly and get very hot. I have checked the diverter valve and both pins seem to be making good contact with the micro switches and moving freely when the hot tap is turned on. Could this still be an issue with the diaphragm or could this be a problem with the plate heat exchanger? I live in an area with very soft water so I wouldn't have thought it to be scaled.

Thanks

 

[ianmcd]

first thing you need to do is measure your flow rate, find something you know the volume of , say it is 10L and it takes 1 min to fill it at full rate then your boiler is set at 10L per min, I know it wont be that easy but the calculation isnt hard, once you know that we can tell you if the boiler is working in HW mode , sounds like it is doing its job but has been set up in the summer when in coming water temps are much higher

 

[dcawkwell]

Plate heat exchanger is blocked with dirt from the radiators so not transferring full heat into the hot water.

Only takes a few flakes of rust to block and it will affect performance.

 

[ianmcd]

normally I would agree with you DCalkcwell but as Op says HW is ok when CH is on suggests that heat transfer is not a problem, not arguing in any way OP

 

[dcawkwell]

normally I would agree with you DCalkcwell but as Op says HW is ok when CH is on suggests that heat transfer is not a problem, not arguing in any way OP

Oh yes I see that with the heating on they do get hot water.

So that would indicate a diverter valve problem not diverting fully to
hot water or is stuck even though the pins are moving.

 

[fruitcake]

Thanks for you fast replies.

That is correct HW works and gets properly hot when the CH is on. If the CH is off it only gets warm.

Could the problem be with the diaphragm then or another part of the diverter valve? It was my understanding that if the pins are moving and operating the micro switches that the diaphragm should be ok.

 

[dcawkwell]

Thanks for you fast replies.

That is correct HW works and gets properly hot when the CH is on. If the CH is off it only gets warm.

Could the problem be with the diaphragm then or another part of the diverter valve? It was my understanding that if the pins are moving and operating the micro switches that the diaphragm should be ok.

If the central heating is off. The water in the radiators is cold.
You call for hot water but because the diverter valve is partially open to
the central heating the boiler is trying to heat a supply of central heating water as well as the water inside the boiler. Result your hot water is luke warm.
When the central heatiing is on the boiler finds it easy to heat the hot water as it has a preheated store of water in the radiators that is being used to heat the hot water because the diverter valve is allowing this in.

Diverter valve at fault.

 

[Agile]

The rear manifold part of the diverter follows the front diaphragm, or at leat it should.

When it becomes dirty it does not move the full travel or even at all.

I find the replacing the whole diverter valve is the best long term solution.

Sometimes in the past I used to clean them but that was never effective for very long so now i just change them.

You can prove this by closing the CH flow valve and then testing the hot water delivery.

Tony

 

[fruitcake]

I see, thanks chaps, makes perfect sense that this would be the cause. I shall close the CH flow valve and test later.

I know you suggested to replace instead of clean but what do you think of the valve repair kits as below? Would save a few quid.

http://www.ebay.co.uk/itm/BAXI-MAIN...073&pid=100015&prg=1006&rk=1&sd=290831072592&

 

[Agile]

I already gave you my views on them.

But as a DIYer whose time is not important or going to be charged for then different criteria can apply.

Tony

 

[fruitcake]

I closed the CH flow valve and tried the hot tap. The water is now not warming at all. Is this correct for a problem with the diverter valve?

I was expecting the opposite assuming this would prevent water entering the CH.

 

[fruitcake]

I dismantled the diverter housing and replaced the valves and both diaphragms. I can see why a plumber would replace the whole thing, very time consuming. There was a small amount of scale inside but the valves were not seized, and we live in an area with very soft water. I put the thing back together and there is no improvement. I also removed the DHW plate heat exchanger and gave in a light tap and rinse and a number of small brown/orange flakes came out. How sensitive are these things, could this light scale be in inhibiting performance?

So I’m in the same situation, hot water only gets warm when the heating is off but works ok when the heating is on.

The only other thing I have noticed is that if I turn the down the flow of the hot tap even when the heating is off the water comes out much hotter.

Any ideas anyone?

Thanks

 

[fruitcake]

Forgot to mention, also replaced the DHW sensor.