Baffled by my boiler! Please help!

[bcoleman]

Hi All,

I have an annoying issue with my combi boiler (fer falcon) in that my mixer shower (manual type from the taps) seems to cycle between being nicely hot and just luke warm.

The flow rate from the cold tap is around 12 l/m and from the hot it's around 7 l/m - although i tested this at night and it seems to be less than this in the morning (maybe because everyone down the street is taking a shower??).

Anyway, what could be causing this annoying fluctation in the temperature? My only thought is that the flow rate could be too low and the boiler is therefore turning itself down to prevent the water getting too hot and then turning itself back on again?

If this is likely to be it, what can I do about it? I've read somewhere in the boiler's manual about there being a flow/pressure restrictor on the cold inlet to the boiler - would removing this help and, if so, where can I find it?? If not, could I turn the DHW temp on the front of the boiler up to prevent the boiler thinkng the water is getting too hot?

Sorry for the long post - just can't work out what's happening.

Thanks for any help you can give.
Ben

 

[Garfeild]

Assuming the boiler is ok,and the plate heat exchanger isnt blocked.

You could be correct in saying that by using the shower, the flow rate may not be quite enough for the boiler to run without switching off/on via the DHW control.
I take it by running a hot tap,the boiler runs nice and steady without cutting out/in again?
I think i would try turning the boiler DHW temp DOWN,then run the shower,therefore using more hot water than cold,giving a higher flow rate through the boiler,it may be a bit happier.
I wouldnt remove any flow restrictors they are there for a reason.

 

[TicklyT]

I don't know if you would gain much by turning the bouler temperature up or down - you've still got to add the same amount of energy to the same total amount of water (hot + cold) to achieve the same temperature at the shower head. If that energy requirement is outside the modulation range of the boiler, then it will still run hot and cold. You may be lucky, and at least it doesn't cost anything to try.

Next on my list would be to try running the shower with another hot tap partly opened to increase the flow through the boiler. If that stabilises the temperature, consider a different shower head with a larger flow rate.

A thorough de-scale and clean of the existing shower head may increase the flow enough to stabilise the temperature

 

[bcoleman]

Thanks for the help - I'll try some of these this evening and see what happens.

This may be a dumb question - but what is it that actually determines how hot the water from the boliler gets? Is it the gas that adjusts when you select the required DHW temp (like on a gas hob) or does the gas remain constant and the boiler just adjusts the water flow through the heat exchanger?

Could the cold water flow in the morning just be so low that it goes through the boiler too slowly and gets too hot?

The flow restrictor on the inlet appears to be optional thing for my boiler and depends on the cold water flow/pressure. How can I tell if I have one and if I need it?

Ben

 

[Agile]

I am not certain that your boiler has a plate DHW HE.

It may well be that there is insufficient flow and after cleaning the shower head then if it still gives a problem you can test that theory by half turning on a hot tap while using the shower to increase the flow through the boiler.

You could also test the flow rate at which the boiler JUST turns on, it shopuld be at about 2.5 li/min.

If the boiler has a temp control on the DHW then what setting is it on?

Tony

 

[lifesagasman]

Assuming the boiler is ok,and the plate heat exchanger isnt blocked.

You could be correct in saying that by using the shower, the flow rate may not be quite enough for the boiler to run without switching off/on via the DHW control.
I take it by running a hot tap,the boiler runs nice and steady without cutting out/in again?
I think i would try turning the boiler DHW temp DOWN,then run the shower,therefore using more hot water than cold,giving a higher flow rate through the boiler,it may be a bit happier.
I wouldnt remove any flow restrictors they are there for a reason.

logical thinking garfield.
i would just add that if your shower is upstairs that's another spanner in the works with extra resistance to DHW flow. you seem to have CCSS (classic combi shower syndrome), like myself and lots of others. everything affects the flow, local mains demand, toilets being flushed, washers filling, ground water temp etc. they all work against combis just when all you want is a nice shower. life's like that.

 

[bcoleman]

Thanks all - will try the various options tonight and see what happens.

If none of them work - would a thermostatic set of mixer taps do the trick or would they also be affected by the boiler apparantly turning off and on?

Ben

 

[transam]

Agile is correct , the fer falcon did not use a plate exc' , I am also 99.9% certain that the max temp of the hot water can be preset by , by either removing or installing a 'jumper' on the pcb , which would limit the H.W to 55 ish , or 65 ish ????? dependant on the jumpers postion , if yiou have a manual it should say ????? dunno if any of thas helps ???????

 

[Agile]

He needs to clean the shower head and measure the flow rates before we need to look at his boiler ( which does not have a plate to clean Garfield. )

Tony

 

[Garfeild]

He needs to clean the shower head and measure the flow rates before we need to look at his boiler ( which does not have a plate to clean Garfield. )

Tony

Ok im unfamiliar with this boiler and didnt know if it had or had not got a plate HEX

 

[bcoleman]

Morning all,

Right - tried turning a hot tap on whilst taking the shower and it didn't seem to make much difference - the temp again seemed to cycle between luke warm and hot - taking about a minute or so to go from hot to warm and back to hot again. Also tried cleaning the shower head with no joy.

What I have now found is that the hot water temp also seems to cycle between warm and hot even when the shower is not being used and just the hot tap is running!

In terms of measuring flow rates - I'm still getting 7 l/m out of the hot and the flow doesn't seem to change regardless of where I set the DHW temp knob on the boiler! Not sure what is going on!!

Any ideas?

 

[dal5band]

Too long a pipe run ? In my son's house we discovered the hot pipe ran from the boiler to the old airing cupboard to pick up the old hot pipes. I.e the hot pipe looped accross the house and back again - this caused some sort of pressure problems causing the boiler to run hot and cold.

Fixed it by re-routing the hot from the boiler directly to kitchen and bathroom above. (boiler in hall - small house)

 

[Agile]

Does anyone know if the pump is meant to run during DHW use?

Luckily I dont see this boiler very often.

I dont think it has any diverter valve and just turns off the pump to stop the rads heating. Can anyone confirm that?

Thats unlike the Puma which has a diverter valve and DOES run the pump on DHW although if its failed it will still give DHW.

Tony

 

[transam]

I am certain that the pump does not run during H.W ,& that there is no divertor valve !

 

[lifesagasman]

This may be a dumb question - but what is it that actually determines how hot the water from the boliler gets? Is it the gas that adjusts when you select the required DHW temp (like on a gas hob) or does the gas remain constant and the boiler just adjusts the water flow through the heat exchanger?
Ben

nobody answered this one yet.

if the flow remains constant as OP says then the gas valve is modulating, yes?
so is it a modureg on this boiler?

a burner pressure measurement during flow would answer quite a few questions here