Vaillant problem

[voodoocars]

Hi. I have a Vaillant turbomax vuw 242/282 combi boiler (approx 12yrs old).It has a few probs and I was hoping someone could offer advice.
The boiler keeps loosing ch pressure- the service valve to the ch leaks slightly so I know about that ,however, the other week I drained the whole system down to do some rad work. Since refilling the dhw does not stay at a constant temp but fluctuates and the boiler can be heard firing up for 10 seconds then off for 10 seconds. When dhw is running the pressure gauge drops right down to nearly zero and the temp gauge goes up to 90' but the water is certainly not that hot.
What is going on? Is the diverter valve knackered.I say this as a few months ago I noticed the rad in the bathroom was getting warm after running dhw.It doesnt now tho'.
Thanks in advance.

 

[Puddle]

Loosing presure through leak as you say
The hot water problem points to the plate heat exchanger being blocked up and divertor valve by passing slightly when on hot water mode to radiators probably due to rubbish in valve,need to remove and clean out items,was water very dirty when you did radiator works?have you been filling/ topping up system pressure weekly?this would cause problem,the pressure gauge problem is pump sucking to hard also pointing to a restriction as above 🙁

 

[voodoocars]

The water was a bit black, yes.I had to replace the auto air vent on top of the pump as this started lealing as soon as I touched it.There was a lot of crusty black stuff in it so I see your point about blocked exchanger.I top it up prob every couple of days- but it doesnt drop to zero.I know what the diverter is but the plate exchanger ? - no idea where that is. If I decide to tackle the job myself is it relatively easy and would I need some sort of service kit? I need to replace the service valve anyway.

 

[voodoocars]

Right, I had a quote from a plumber of £220 to drain and replace the heat exchanger and service cock.He said that the HE is blocked but it would be more cost effective for him to swap it rather than waiting to de scale it.(HE - £104, service cock £57 [😱]).He recons the divertor is ok.I've noticed that the pressure relief valve to outside is dripping as well - can these be adjusted or is it easier to change? I'm willing to have a bash at this to clean the HE and do whatever but I fear that once its apart I'm gonna need extra bits (washers etc) and the missus is bitin' my ear off at the moment🙁. Its not that difficult is it...

 

[knsbuilder]

I had that problem and by checking pressure in the expantion vessel where there is a bycycle cap fits, remove it, check pressure and fill according to the manufecture instruction and see if it works. As per radiater getting hot in the bathroom, i had same problem and engineer checked the diverter valve, it was gone the lime scale did it duty and it was totally jamed could not be pull or push so after changing it was solved.

 

[knsbuilder]

Thanks after reading every message, i now could think about heat exchanger and after looking into the manufecture manual, it look like small steel plate around 3 wide by 6 inches long very bright looking where few steel plate are joined together and it looks though work to me and without engineer advise, winter approaching so i have to wait and see.