0.4 Bar system pressure drop when pump starts

[ivanov]

Hi,

I have sealed central heating system with Keston condensing boiler. I've drained the system recently and refilled it. I've also set my EV pressure to ~1Bar (15psi) when the system was drained. After I've bled all the rads and pump few times I'm experiencing the 0.3-0.4 Bar instant pressure drop (from 1.2 Bar pressure when it is cold) when the pump starts from cold. Could you pl;ease advice what is causing that?

Thanks

 

[ChrisR]

Pressure gauge is on the input side of the pump (I assume). If it were on the output side, it would go up when the pump starts.

 

[ivanov]

Chris the pressure gauge is at the EV which is at the input site of the pump but is the water pressure drop of 0.4 bar normal? The reason I'm asking is that before I drained and refilled my CH this was not happening. The only difference that I can recall is that I increased the Air pressure of the EV which was lower before, to 1 Bar. Can this cause the water pressure to behave differently?

 

[ChrisR]

To be honest I can't see why it should have changed, unless there's a little bit of air stuck somewhere critical - or something. But it's quite normal to see the pressure go up or down by 0.3 - 0.4 bar with the pump.
Is the pressure at the same as it was before you drained - they aren't as sensitive at lower pressure, usually.
Keep an eye on it but I wouldn't worry. Keston would know the idiosyncrasies of the model of course, they're very good tp speak to.

 

[ivanov]

It seems to be the air which I can't get rid of unfortunately. I've done everything that I'm aware of:

Step 1. Drained and refilled the system by bleeding all the rads and a pump also ensuring that the auto air vents are not shut.

Result: CH was working fine for 2 days and after that some of the upstairs rads start bubbling

Step 2. I've closed all the rads valves except one (only upstairs) at the time and started the pump with the boiler OFF. The initial result was bubbling at the open radiator. Stopped the pump, bled the rad and so on for all the rads upstairs.

Result: CH works fine no bubbling rads at all UNLESS I SWITCH ON THE BOILER. After the boiler was switched on the same old story bubling rads upstairs.

Step 3. I've done the same excercise as in step 2 but with the boiler ON. After which i was able to get some more air our from the rads.

Result. When I switch the CH and the boiler ON bubbling rads more that ever.

Step 4. I don't have any obvious leaks but I decided to add Fernox leak sealer but still didn't fix my problem.

Am i doing something wrong or can someone advise me of something that I'm missing in order to get rid of the air in my CH.

Thanks in advance for your help

 

[ivanov]

Is the pressure at the same as it was before you drained - they aren't as sensitive at lower pressure, usually.

Chris the pressure was lower that before 1Bar vs 1.4Bar. However when I topped up the water pressure to 1.4Bar then I don't see such a big drop (I would say 0.1 max). Is there any relation between the water pressure and the pressure drop when the pump starts?

More over now that I put the pressure to 1.4Bar (after all the things I've described in my previous post) I don't hear the bubbling noise in the radiators but I don't think it will stay like this for long .

I don't know what is going on with my CH