Vokera compact 28 - water keeps running hot and cold

[neilianos]

boiler been working fine, then out of blue the water runs hot, then col, then hot then cold etc which is annoying and dangerous when in shower.
also the pressure is right in the red indicating 4 bars

Any ideas???

 

[Agile]

Well sort out the pressure first and then we can look at the hot water!

See FAQ on this site.

Tony

 

[neilianos]

I did, i blead a radiator to get it back to normal, but the problem still remained

 

[Agile]

There can be several causes and some are gas related which we cannot advise on here.

I assume you dont get any lights on the boiler? You could measure the resistance of the DHW sensor but probably need to monitor the voltage across it when using DHW to see if its become incorrect.

Tony

 

[neilianos]

the green light is on and everything is ok normally, but the water just keeps going hot and cold and no matter how many times i keep letting water out of the radiator, the pressure keeps going up to 4 which is wierd, because i thought if it got to 3 it released the pressure itself?? Which is what it dd in the past when i had a problem with expansion vessel

 

[Egga]

It looks like you may have more than one fault.

 

[Agile]

Do read the FAQ.

It seems the filling valve may be leaking!

Tony

 

[ecowarrior]

hot & cold is plate heat exchanger blocked causing boiler to cycle.. Over pressure will be filling loop letting by. If its not blowing at 4 bar there is so much carp in the system not only has it blocked the HX but also stuffed the press guage.

 

[nickso]

hot & cold is plate heat exchanger blocked causing boiler to cycle.. Over pressure will be filling loop letting by. If its not blowing at 4 bar there is so much carp in the system not only has it blocked the HX but also stuffed the press guage.

Unlikely it's the Plate H/E...it doesn't have one.

Also, the pressure guage on a compact is so inaccurate you might as well use a divining rod to tell if there is anything in it.

 

[justqualified]

Your pressure problem is most likely to be the twin pass heat exchanger allowing mains to over pressurise the heating system, if you close the black square plastic valve under the boiler on the right hand side and drop the pressure by bleeding a radiator to 1.5 and monitor it, as for the hot/cold it may be the thermistor but check if the green light stays solid all the time or flashes when water is running as flame may be cutting out but thats a rgi problem.

 

[beebee]

I have a whole story to tell that might help you:

Pressure kept dropping so kept topping up plus pressure would rise quickly when heating came on. I was told the pressure release valve was leaking from debris and the expansion vessel had gone. Changed the safety valve - not too hard, cost about £15, but made no difference to pressure fluctuation.

In parallel, debris managed to block bend in outflow pipe into central heating circulation causing no hot water in radiaters and water constantly circulating from HE to pump and back to HE. Took the pump out and unblocked the blockage. Got central heating back.

Then had it serviced by someone who was not competent. He set the minimum gas pressure to above the maximum. Hot water was coming very hot, very cold, very hot. Or just very hot then cold only as boiler was cutting out - I guess from overheating. The boiler couldnt regulate the flame.

Kept loosing pressure in central heating and eventually flat mate who kept topping up the system broke the tap on the feeding loop so it was feeding water into central heating constantly and pressure release valve was releasing it constantly - with lots of loud banging noises. Pressure in system remained 2.5 to 3 all along. I wondered what was going on for a while, then noticed the feeding loop and closed it with plyers. For a night the system ran OK with large pressure fluctiations and lots of banging and hissing, but by the morning the pressure had gone.

Then got a more competent plumber from vokera to check it:
Turns out only the tube to the expansion vessel had blocked with debris - quite easy to clean out. The pressure is now pretty consant and not disappearing.
He set the gas pressures correctly and changed the thermister which was covered in debris. More constant hot water temp now.
Only problem is that overheating HE has lead to scaling inside causing lower hot water pressure and inefficiency - my next project. Any advice anyone?

 

[ianmcd]

There can be several causes and some are gas related which we cannot advise on here.

I assume you dont get any lights on the boiler? You could measure the resistance of the DHW sensor but probably need to monitor the voltage across it when using DHW to see if its become incorrect.

Tony

yet again the usual Tony Reply on here "you need an RGI so we cant advise " Tony it is a system pressure problem !!!!! read the thread for fecks sake