Air in the system??

[ComedyPhil]

I recently had a new boiler fitted as well as a new 2 way valve. Since starting the system, I have had to bleed one of the upstairs radiators daily.
Last night I noticed that the pump was running dry. I bled the pump and the bleed valve, as well as the radiator again.
I checked the header tank and it was quite full (3/4) with warm (almost hot) water.
I let the system cool down, switched it back on and it ran OK again.

We hadn't been using the system to heat the hot water until we got the valve replaced (used immersion heating element instead) and it must be said that when both the water and heating are on, you can hear the water flowing through the system quite loudly (a gushing sound)
I know the sensible thing would be to get the engineer who fitted the boiler back out to have a look, but there was a breakdown in trust with him as he kept trying to scaremonger me into additional jobs, most of which I knew were not necessary (at least not without ruling out other things first)

I am a mechanical engineer and a qualified toolmaker, so am fairly handy.
I would like to know if anyone has any advice on things that they think it could be?

Thanks in advance.

 

[kbdiy]

If the header tank is filling up with hot water then you have 'pumping over'. Can be a number of causes - blocked cold feed where it joins into the system; sludge/blockage elsewhere; pump speed too high; incorrect pipework.

If the pump is running dry yet the header tank is full then my first guess would be the blocked feed.

Possibly the 'additional jobs' your plumber spoke about were more necessary than you believe?

 

[ComedyPhil]

Thanks very much for your reply, I will set about checking the cold feed and the pump speed first.
One of the things the plumber wanted to do was change the pump. This was without seeing it running (he said "that pump looks dodgy and could contaminate your boiler" - When challenged, he couldn't tell me why (the pump is clean and operates quietly without any evidence of wear or malfunction)) or checking anything else (He didn't even go into the loft!)
As I said, I am a mechanical engineer, so although I am not an expert on CH systems, I do know a malfunctioning pump when I see one.
I believe he saw it as an easy way to add a few hundred pounds onto the bill.
In hindsight, I should have been suspicious that he didn't check the entire system before giving me a diagnosis/quote for the boiler - but we were desperate to get it sorted.

 

[kbdiy]

Did he carry out any cleaning/flushing of the system before commissioning the new boiler? If not then a blocked feed is high on the list of suspects along with the fact that the rest of the system would benefit from flushing.

 

[ComedyPhil]

No cleaning or flushing, in fact like I said, he didn't even check the header tank in the loft.

 

[kbdiy]

That pretty much sums it up then. Start looking for that blockage. You may end up having to cut a section of pipe out unless you can find a way to force the blockage out.

My own system had a considerable build-up of sludge at the point where the cold feed entered the system pipework. With the boiler turned off I emptied the header tank and cleaned it out first. Then closed of the pump valves so no water could pass beyond that point, pushed a hosepipe up the vent pipe as far as possible and turned it on full blast. That pushed the blockage back up into the header tank. I kept flushing and emptying until I was satisfied it was clear.

Worked for me but I know my pipework layout so was confident in my theory.

After that I treated the system to some Sentinel X800, ran it hot for a few hours then fully flushed. Fitted a Spirotech MB3 filter in the return just before the boiler, refilled with inhibitor and working well ever since.

 

[45yearsagasman]

View media item 39013
That's a typical open vented pipe configuration. Use a magnet in the area of the feed and vent connections to detect the area of blockage. Have you noticed water pumping out of the vent pipe into the header tank? If you detect blockages, chemicals will not work and as said the correct way is to cut out and clean/replace the pipes.

 

[ComedyPhil]

Thanks all, given me something to work with.

 

[ComedyPhil]

Thanks everyone, confirmed with the "engineer" last night that he switched the pump onto full speed (couldn't tell me why) so I turned it back down. I have left the system off overnight to completely cool down and will bleed and test it tonight. I couldn't find any "magnetic" blockages but that is not to say I was checking in the right place. If it is still not right this evening, I will probably have to have it power flushed (probably best to do it anyway). Is this something that people on here could vouch for? I have recieved quotes for £300-£325 incl. Does that sound reasonable?

 

[45yearsagasman]

A power flush will not move hardened deposits. The only way is to find it and cut it out.

 

[Spiderpig]

>I checked the header tank and it was quite full...

I had problems with my system filling with air and cutting the boiler out because as part of some 'improvements' (mainly cleaning) I had increased the depth of water in the header tank because it looked a bit low. After a lot of investigation and messing about I tried lowering the level again to just a couple of inches above the feed pipe hole and no more problems with air, no more bleeding rads & pump. It really was that simple!

 

[kbdiy]

I suspect it may not be quite that simple. It seems as though the pumping over was occurring when the pump speed had been increased and therefore overfilling the header tank.

Since you have now reduced the speed it may have cured the pumping over but doesn't necessarily mean that the problem has gone away, rather that it is being masked by the lower speed and the pump's inability to force water past the blockage (maybe only partial) and into the header tank.

That is just my suspicion anyway - having experienced similar in my own system. Now the blockage has been cleared from my system I can run the pump at full speed and not encounter any pumping over problems.