Voker Unica HE - Hot Water but no Central Heating?

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Hi Everyone,

I've been struggling with this for a week or so now and after reading a few similar posts, I thought I would see if anyone could give me a little bit more advice. I apologise in advance as there is a little bit of a backstory to this.

In December our hot water started going hot/cold/hot/cold and the temperature readout on the boiler was rocketing up and down. I had Homecare cover through British Gas so after getting an engineer out they said the heat exchanger would need to be changed due to dirt in the system and I would be quoted for a powerflush, magnaclean the lot. A week or so later the engineer returned to change the heat exchanger (unfortunately I wasn't here so didn't see exactly what was done) and a note was left saying there was dirt in the system and would need a powerflush.

The British Gas experience was awful (not the first time) so I have promptly cancelled my Homecare package in favour of seeking a local plumber for a powerflush and any future repairs.

The hot water problem was resolved but we soon found that the central heating would not come on - The click would come from the receiver (Hive) but the boiler would not act on this call to heat, however I soon found that this was resolved by running the hot water which seemed to kick the boiler into providing central heating. This worked a few times but unfortunately is now working a lot less if at all...

When the boiler is in this state of providing hot water but not igniting for central heating there is a constant noise present which only changes when calling for hot water and then returns to a drone which I think is some sort of fan (tacho fan?). This is noise is present in all modes eg, Hot Water Only, Central Heating etc.. and only switches off when the boiler control is in the off position or if the "switching on the hot water" solution I mentioned earlier has worked.

I have taken it upon myself to try and resolve this issue as I have been unable to get a decent local plumber out as they all appear to booked up for a good while.

My first thought was the divertor valve actuator or valve itself. Manual operation of this valve (with the actuator off) makes no difference and for good measure I purchased a replacement actuator which has made no difference (I have since confirmed my old actuator is perfectly fine). I have also made sure there is no air in the system by bleeding all the radiators and the pressure is at its usual 1.5 bar.
I should probably add there are also no error codes or lockout conditions occuring.

My current line of thinking is that it's thermistor/ntc sensor of some kind as after a test an hour ago I noticed that when the boiler was powered back up and after running some hot water the temperature gauge rocketed up to around 70 which makes little sense as no water was being called and the central heating was off. My only logic behind this is that a temperature sensor is goosed making it think the boiler is crazy hot and not allowing the central heating to fire because of this although this is where I need a little as I can't find any evidence of this in the service manual...

Thanks a lot for reading this very long post and I appreciate any help anybody could give me.

UPDATE: Left the boiler off (on the controls not mains) to see if this helped. Turning it back on resulted in the droning noise coming back and the temperature flying up to 70 odd again. Turned hot water on/off a few times - Drone noise went, temperature read 51 and central heating could be ignited...
 
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I am not that familiar with vokera boilers ,so maybe not the best person to be advising you. The boiler does appear to be firing up on demand and the temp rises to 70 ,even when domestic hot water taps are not open , if I have understood your post correctly. If so ,you then have a circulation problem ,as the heat being generated
Is not being dispersed. Check the pump function.and the diverter valve may be at fault ,blocked up.
 
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I wonder whether one or both of the isolating valves on the heating flow and return are closed. They're the two on the left and are a quarter turn off to on. Also how are you checking the diverter valve cartridge? To get the htg flow remove the actuator and push the pin in. If this doesn't work look at those valves
 
Thanks for your replies.

While the divertor actuator was off I did push the pin in which moved quite freely. I could hear water moving around when I pushed the pin in but the boiler still did not fire.

I did think it could be the flow return pipes - would these have been turned when the heat exchanger was changed? The problem I had is I wasnt sure which way to turn them as the screw head wouldnt budge and the other side was incredibly free to move - does this look normal to you guys?
 

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I would be looking at the diverter valve cartridge, they are common to break up inside
 
I would be looking at the diverter valve cartridge, they are common to break up inside

Thanks Ian - If i was to change that cartridge would I have to drain the system down? Probably an obvious question just don't want to remove something and get an unrequested shower...
 
you just need to drain the primary water in the boiler, no need to turn off the cold water inlet, there is a drain point on the lower front of the boiler, dont touch the isolation valves or the PRV, its a very easy job to do, if the cartridge is broken up use long nose pliers or similar to make sure you have got all the pieces of the old cartridge out , as said a very easy job
 
Hi Everyone,

Very late in the response to this but I thought I would get back and let everyone know the solution - Who knows, It may help someone out in the future!

After trying the diverter valve replacement which unfortunately didn't work and after being unable to get hold of any local plumbers I trusted due to them being snowed under with work I signed back up with Domestic & General Boiler Cover for a years cover and the fixing of the current problem.
I had previously had Domestic & General and I must say I never had any issues with any of the fixes I had, they send either Vokera specialists or other plumbers to resolve the issue who are just there to fix the job, so no British Gas up-selling or nonsense!

The engineer attended the next day and resolved the problem in 45 minutes - It seems the actuator valve had failed, he replaced this part and everything was back to normal!

It has and will cost me around £20 a month for the next 12 months but it got me out of a tight fix as I just didn't have the time to get back on a night from work and replace the parts till I finally got the right one but at least I'm now covered for a year and to be honest I think I'll go back to Domestic & General for their boiler cover in future.

One thing I have learned from this experience is that I will never trust British Gas with their HomeCare cover ever again! I don't have a problem with the engineers as for the most part there alright but the whole British Gas support model just seems to lean more towards we would rather replace than fix which for me is no good.

Thanks to everyone who pitched in with this one, I really do appreciate it!
 
What is the "actuator valve". I have a similar problem with Vokera Vision boiler (enclosed system not combi), that is to say water heating in the boiler but no circulation and I have already replaced the pump and bled air from the boiler. I have cleaned the Fernox TF1 filter so that is not restricting circulation. I am going to replace (or inspect) the return inlet valve and flow outlet valve (same as in your photos) as they do seem very loose ie like nothing inside is turning when you turn it, and both drip. Are these what you mean by the actuator valve(s)??
 
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What is the "actuator valve". I have a similar problem with Vokera Vision boiler (enclosed system not combi), that is to say water heating in the boiler but no circulation and I have already replaced the pump and bled air from the boiler. I have cleaned the Fernox TF1 filter so that is not restricting circulation. I am going to replace (or inspect) the return inlet valve and flow outlet valve (same as in your photos) as they do seem very loose ie like nothing inside is turning when you turn it, and both drip. Are these what you mean by the actuator valve(s)??
your boiler doesnt have a diverter valve or actuator, you really need to start your own post
 

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