Getting very little Hot water from Heating System

footfall789

Hi , have a oil fired boiler that is used to heat the Radiators and hot water

Radiators work fine , radiators are hot ,the problem is with the hot water . I turn on the boiler and Hot water seems to heat up fine after 20 mins and I turn off the Boiler . I then turn on any hot Tap in the house and it runs hot for about 45 seconds and then goes cold . The funny thing is that if I turn off the tap for about 10 minutes and turn it on again I have hot water for about 45 seconds again ( the boiler is still off) .

I also have an immersion heater that I tried without having the Boiler on and the same thing happens i.e turn on immersion for about 20 mins , turn it off , turn on any tap in the house and I have hot water for 45 seconds and then the water runs cold again . I turn the tap off for about 10 minutes and then I will get Hot water for about 45 seconds again and it runs cold again .

Checked the pipes at each side of the motorised valve for the hot water and both are extremely hot to touch.

Any ideas on what might be the problem .

K.Flyer

Go up into the attic and check that the end of the pipe that hangs over the large cold water storage tank is not in the water. If it is, carefully see if you can lift it out of the water, a couple of inches is enough and try the taps again.

scudo2

K.Flyer wrote: »

Go up into the attic and check that the end of the pipe that hangs over the large cold water storage tank is not in the water. If it is, carefully see if you can lift it out of the water, a couple of inches is enough and try the taps again.

I was just about going to say that too.

footfall789

Thanks for getting back so quickly , have never been to where this is located in the Attic but will go up there to see if i can find it . Based on the fact that I know nothing about plumbing ,would the cold water storage tank not be enclosed to stop any stuff getting into it e.g flies , dust e.t.c .

Will let you know how i get on . thanks again for reply.

footfall789

Hi Went up to Attic again but cold water tank enclosed , Opened up and only saw a balcock and machine on top of Tank (showing pressure of 2 bar on it)with pipe pushing through top of tank into water.

Any Ideas.

Nino Brown

K.Flyer wrote: »

Go up into the attic and check that the end of the pipe that hangs over the large cold water storage tank is not in the water. If it is, carefully see if you can lift it out of the water, a couple of inches is enough and try the taps again.

Just out of curiosity, what is that pipe and why would it cause that problem?

scudo2

footfall789 wrote: »

Hi Went up to Attic again but cold water tank enclosed , Opened up and only saw a balcock and machine on top of Tank (showing pressure of 2 bar on it)with pipe pushing through top of tank into water.

Any Ideas.

Photo please if that's possible, Ta.

Dtp1979

scudo2 wrote: »

I was just about going to say that too.

Me too

Dtp1979

Nino Brown wrote: »

Just out of curiosity, what is that pipe and why would it cause that problem?

It the vent pipe. When a hot tap opens, cold water sucks of syphons from the tank back to the tap. Of course this won't happen if the pipe isn't submerged into the tank.

esox28

Id say you have a submersible pump located in the tank in the attic. Would I be right in saying you have no hot water cylinder and a combi gas boiler

footfall789

Hi yes its a submerged pump in cold water tank in Attic.
I have an Firebird c44 condensing Oil Boiler ,

A bit of History, the last couple of weeks we have been having problems with the hot water going hot and cold and back to hot again both with showers and on the sink taps. We have a Mixing valve and thought it may not be at high enough setting with the cold weather and all . So beginning of this week moved Mixing Valve to MAX(Hot) setting but still no luck then on Friday I started having this current problem where hot water would come on for 45 seconds and then going cold .

So I moved the Mixing valve to every setting but no change , am wondering if this is the problem and the mixing valve is faulty and its mixing incorrectly.

Dtp1979

esox28 wrote: »

Id say you have a submersible pump located in the tank in the attic. Would I be right in saying you have no hot water cylinder and a combi gas boiler

Well spotted

esox28

Yea sounds like the mixing valves calabrations off.

esox28

Dtp1979 wrote: »

Well spotted

sound. But I've fitted loads back in the day, never much rated the set up but 10 years on and not one call back on the pumps the immergas boilers on the other hand well I don't need to tell ya.

whizbang

Are there filters in the inlets of this mixing valve ?

esox28

Actually there is or should be on both inlets what make is it?

footfall789

Hmm, unless the filters are in the Mixing valve itself then, no there are no filters on the Inlets to the Mixing valve .

Is it easy to remove and replace , my preference would be just to remove the silly thing , as I have a Temperature Control on the hot water tank that goes to the Boiler which I can set.

The Mixing valve is a Giacosun r156 max 100 c.

scudo2

Nino Brown wrote: »

Just out of curiosity, what is that pipe and why would it cause that problem?

Miles ahead of me, fair play to you, good call. I tip my hat.

Sorry I included wrong section.
My hat tipping is for esox28 brilliant call.



(No offense to Nino intended)

whizbang

I have a Temperature Control on the hot water tank

Hmmmm...

whizbang

OP, dismantle and flush out the mixing valve, refit and let us know whats what.

footfall789

Not a plumber I am afraid. Would I not have to drain system first and then remove the mixing valve . If this is the case then how would I drain the system .

Thanks

whizbang

You would turn off the cold supply from the attic storage tank. There may be more than one. Then run off the hot and cold water from the taps. Your kitchen sink cold supply may be fed from mains.

However, I would go back and check if the mixer is restricting the hot first, by feeling the temperatures of the pipes into the valve, after the hot water has run out.

esox28

There should be isolation valves on the mixer just turn off the cold side.

If there isent isolate the main cold supply to conferm its the mixing valve fault, you should be able to just have hot water runnning.

whizbang

The mixing valve should shut off the hot if its above setpoint, and there's no cold supply.

esox28

Mixing valves rarely completely shut the hot off, even when new and especially when pdhw is used.

footfall789

Hi All, mixing valve was the problem all right . Once it was removed the hot water flow was fine . Will have to invest in a new mixing valve in the new Year .

Thanks for your help , Merry Christmas to all .