combi bioler dhw heat x

[spudy]

Hi, new to the forum ( first post ) have tried to search but could not find the topic , so hear goes . I have a Keston C36 its about 7 years old and the hot water produced is not as good as it should be . I am wondering if the DWH plate heat X is not as good as it should be , the keston shows the primary flow temp and DWH temps on the control panel the difference betwwen the two is round about 18 deg c . The question (finally) is this ok or should i suspect silting up ? thanks in advance regards to all .... :

 

[Dan Robinson]

What do you mean "should be"?

It's a Keston. Be grateful that it is doing anything more than hanging on the wall fizzing and crackling electronic death at you.

 

[spudy]

Thanks for the reply Dan , by should be i mean not as good as it was and was wondering what the acceptable heat in heat out should be for this type of heat x . I've heard all about the keston bad rep but to be fair to this on its been ok so far , i know its struggling to reach the 35 deg c temp rise at tha stated flow of 15 lpm , regards .....

 

[ALCPlumbing]

If the hot water has got progressively worse than it would certainly suggest that the plate to plate is getting scaled and sludged up. Is there a scale reducer on the water main before it connects to the boiler and any kind of magnetic filter on the heating return?

7 years with a Keston and no problems must be some sort of record.

You may find that the diverter valve is letting by and as a result the plate heat exchanger is not getting the full flow from the main heat exchanger. You can test this quite easily. With the heating off run the hot tap and feel the flow pipe to the heating (usually the pipe furthest to the left under the boiler). If it starts to get hot then the diverter valve is letting by and needs to be replaced by a Registered Gas Safe engineer. Let me know.

J

 

[spudy]

Thanks for the reply J,

Its a bit of an unusual one the best way i can relate to it as a motor mechanic is when an engine is running ok but its not quite 100% and you can't put your finger on it . Its had a new heat x , flush and fernox T1 filter about 6 months ago , my brother is Gas Safe registered and very experienced and is having to think about this one . The central heating is fine the hot water is ok but i don't think its a it should be .The flue gas has been analysed and is ok the only thing that does not look correct is when the meter is timed it is showing that the boiler is using 2.75 M3/hr and should be 3.75 M3/hr when the hot taps are on full . The gas pressure is ok so my brother is going to contact Keston for advise but in the mean time i thought it a good idea to ask for other opinions to help out ( i do his van he does my gas ). regards....

 

[Dan Robinson]

These ****boxes also had mesh filters on the primary side of the plate heat exchanger which may have clogged up.

Poor flow through the primary circuit will reduce the heat input.

 

[spudy]

Hi, Dan thanks again ,

pretty sure the filter was removed after the flush and new DWH heat x and fernox filter were fitted . When you say low boiler input do you mean it could be the reason for the meter timing being out , regards....

 

[Dan Robinson]

Yep.

 

[spudy]

Hi, Dan Thanks,

so the primary heat x could be blocking up, would that not cause the boiler to over heat as it did when the DHW x blocked up , i am not doubting your diagnostics i just like to understand if i can , regards....

 

[Agile]

Your boiler is only taking about two thirds of the heat input.

That means it will only give about two thirds of the heat output.

A poor or blocked pump or a flow restriction within the boiler are all possible causes.

Tony

 

[spudy]

Hi Tony thanks for your reply ,

Just to check i have understood the low gas rate could be caused by a reduced flow through the primary heat x , which could be a slow pump or a restriction in the primary heat x . Instead of over heating and locking out the boiler is modulating down the gas input to match the flow of CH water through the boiler . Is there any way to confirm if its the pump or a partial blockage , regards ....