Ravenheat RSF 84et- Hot water not not enough!!!

[rizy102]

hi,
CH works perfect. really hot. however hot water is a nightmare. if you open the tap full then basically the hot water is just about warm. if you reduce the water to a trickle, then hot water comes out of the tap. had a plumber come round and he suggested my water flow was too high for this kind of boiler. he said i would have to get a new one! however, i remember having very hot water when the boiler was fitted approx 5 years ago.
i've changed DHW sensor, diverter valve, and microswith, but still no luck.
anyone have any ideas?
thanks

 

[Agile]

Wonderful how you blindly change so many parts!

Have you actually measured the hot water flow rate?

If so what is it?

Then compare it with the specifications quoted for your boiler.

Tony

 

[gas4you]

I would think you should get a 35C temp rise with about 9-10 litres/min flow.

Oh and get another engineer in for a 2nd opinion if the above doesn't correspond to your results.

 

[rizy102]

hi, the flow rate is 9 litres/minute.
i have no idea what specs are quoted for my boiler. does anyone know?
thanks

 

[Slugbabydotcom]

Try a CH sensor first. If you don't fancy blowing another £15 just use your old DHW sensor. Chances are there was nothing wrong with it.

DHW potentiometer is a rarer possibility. Once had one with a faulty connection on the plug where it connects to pcb.

Theres a flow regulator on the DV if you fancy a play about with that although at 9 l/min you shouldnt need to.

D.H.W. FLOW RATE 30 ºC rise 11.7 l/min (2.6 galslmin)
D.H.W. FLOW RATE 35 ºC rise 10.1 l/min (2.24 gals/min)
D.H.W. FLOW RATE 40 ºC rise 8.8 l/min (1.96 gals/min)
10 ºC inlet temperature

A decent corgi engineer could use the following info to check that theres nothing going wrong with your gas supply.

GAS RATE AFTER 10 minutes
max 2.6 m3/h (91 .8 ft3/h)
mid 1.9 m3/h (67.1 ft3/h)
min 1.3 m3/h (45.9 ft3/h)
INLET PRESSURE 20 mbar (8.0 in w.g.)
BURNER PRESSURE
max 8.1 mbar (3.2 in w.g.)
mid 4.0 mbar (1.6 in wg.)
min 1.5 mbar (0.6 in w.g.)

 

[rizy102]

hi,
thanks for the replies.
i thought about changing the DHW potentiometer, but when i move to min position the water goes cold. i.e. it works accordingly if i play with the temp. is there still a possibility i would have to change it?
thanks

 

[Agile]

I dont think that you have measured your flow rate!

You measure it at the bath tap, not in a book!

At 9 li/min you need to measure the inlet temperature and the outlet temperature and see if its about 35 C difference!

So far there is nothing indicated as wrong with your boiler!!! Apart from your expectations that is !

Tony

 

[rizy102]

i did measure it at the bath tap. in 1 minute it produced approx 9 litres.
in my other house i have the same boiler and it produces 10 litres in 1 minute and the water is basically too hot to touch if you put the potentionmeter to max.

 

[Slugbabydotcom]

I would put a new ch sensor in first cos they are 'what goes' on these. If you dont then you are unlikely to have a level playing field to sort the rest out. If it ain't a problem now it will be sooner or later so you have little to lose.

HW and CH potentiometers are the same so you can either swap them over using small connector blocks or compare the max resistances. Beware the aforementioned dodgy pcb connection plug.

 

[Agile]

i did measure it at the bath tap. in 1 minute it produced approx 9 litres.
in my other house i have the same boiler and it produces 10 litres in 1 minute and the water is basically too hot to touch if you put the potentionmeter to max.

And what about the temperature rise?

Next we want you to measure the gas consumption at the meter.

Tony

 

[rizy102]

@Slugbabydotcom.
i have also changed the CH sensor but just forgot to merntion it. also, ill try the potentionmeter.

@Agile
what do you actually mean by check at the meter? would that be the mains gas meter? if so it takes (with the hot bath tap on) either 0.045 m3 a minute, or 0.45m3 a minute(i dont really know how to read the meter but there was a 045 change in the red rectangle bit). is that correct or did you mean something else.

thanks

 

[gas4you]

That sounds about right to me, equates to approx 2.4m3.hr which is what 80,000 btu combis draw approx.

 

[Slugbabydotcom]

Gas rate is fine. With the heating system cold run your bath tap again for a few minutes.
If the Heating flow pipe gets hot then theres a problem with the diverter valve.

 

[Agile]

Isn't this the one with a four pipe heat exchanger???

If the gas rate is correct and the DHW flow rate is at the specification 9 li/min then scaling of the HE is the obvious cause unless its heating the rads as well.

Tony

 

[rizy102]

right, i think ive found the problem. as suggested i checked if, with CH cold, heating flow pipe got hot when i switched bath tap on. and guess what. yes it did!!! so now i have to go and replace my diverter valve. hes obviously sold me a dud!!!

thanks to everyone who replied. this forum really is great!!

p.s. ill confirm again when the diverter valve is fitted.