Vaillant Ecotec 837 combi hot water noise

[icewinder]

I had a problem before were the central heating would make a noise when heating up but after having the system serviced, cleaned and bled all the rads all's well till last night.........

The hot water now makes a terrible noise when we turn a hot water tap on. The temp for the hot water is set to 62 degrees but after a few seconds of the taps been on it makes this noise similar to what the heating use to do , it's like an aeroplane taking off , a droning noise.

I tried everything lowering the temp of the water but that's no good as its luke warm so I then lowered the actual water inlet via the stop cock under the sink.
I ran the hot water and then, ever so slightly kept turning the stop cock anti clockwise/off till the noise stops while the waters running. The problem I have then is the water flow on the hot tap is very slow and if you put another a tap on at the same time it becomes no more than a trickle.

Also with the flow set low the taps splurt when I turn a hot tap on , just thought I'd mention it. Might sound a stupid question but, can you get air stuck in the hot water system or the cold feed to the combi ?

anyone help please .

 

[Agile]

You have not told us how old the boiler is, if it was professionally installed or what the radiator or heating load is or what the RGI who serviced it says.

Your problem is often caused by dirt in the main heat exchanger. I try chemically cleaning these but that is not always 100% effective and replacement may be required.

Tony

 

[icewinder]

3 years old,
service guy said all was well at the time a few months back but this hot water problem only just started.,
yes professionally installed on old pipework but was flushed before hand and new rads installed,
Has been recently drained , cleaner added for a few weeks then drained and inhibitor added and was working fine till the other day.

 

[Agile]

If it is dirt in the main heat exchanger that rarely seem to be cleared by normal cleanser added to the whole system.

Its gets worse. That model usually has a heat exchanger with four parallel sets of tubes so any effort to clean it means that the flow goes through the clear tubes and little if any goes through the blocked parts!

Has this plumber seen it in the current state?

But perhaps some of the others will comment later.

Tony

 

[icewinder]

I'm not very good with the inner workings of a combi bolier but why does it do it on the hot water but not on the heating when it comes on from cold ?.

 

[Agile]

You have not told us how old the boiler is, if it was professionally installed or what the radiator or heating load is or what the RGI who serviced it says.

Tony

You never told me the heating load.

Your boiler is capable of over 30 kW of output but its unlikely that you live in an eight bedroom house so lets assume a three bed semi which is usually about 10-12 kW.

On hot water the whole boiler's heat output can be used.

On heating it will be about a quarter of the full power so working at a small fraction of the max power.

Tony

 

[icewinder]

something that really baffles me is the VRT-392. I would say after months of study this mini PC I got to the basic grips with setting it up for timing the GCH on/off.

So lets say I set the temp of the water to 62 degrees from the VRT-392 downstairs directly below were the boiler is located upstairs. The temp dial for the water is set to max as the VRT-392 takes over I then run a hot water tap.
If I then look at the LED display on the boiler itself it starts to go into 72-73-74 degrees and the boiler begins the droning noise. If I move the dial back to say 5 past is quietens down and the water remains the same temp so whats going on there ?.

surely if the VRT-392 takes over the water temp when in operation the boiler should not show 70 odds on the boiler display panel , it should show 62 degrees like I set it to downstairs, am I wrong or right ?.
By moving the dial back to 12 o'clock on the water it stops. I don't get that.

Its like the VRT-392 tells the boiler the temp its set to and the boiler lets the water run at that temp but the boiler LED displays 70odd degrees and starts to run overtime to get right up to a max but the water never reaches 70odd as I can stick a hand under thew water .....wierd