I've broken the central heating, mother-in-law here!

[Rab]

I've drained my open-vented gravity fed pumped system to fit Danfoss RAS-C2 bi-directional TRVs upstairs.

The TRVs are now fitted, and I've turned the water back on to the cold water feed cistern, but my upstairs radiators didn't fill up after a day (i was bleeding all the radiators, but no air was escaping), so i guessed the system has airlock.

I've reconnected my hosepipe to the draincock downstairs, and tried to fill the system bottom-up. It seemed to start working as air was escaping when bleeding the upstairs radiators, but this became incrementally less with each bleed. I've been filling for two hours now.

We've got no hot water and no central heating. My mother-in-law has arrived, and my father-in-law arrives tomorrow. No central heating engineers or plumbers are available in the area for the next week.

Has anyone any suggestions? Could this possibly be related to the directional setting on the TRVs? From what I've read, the direction doesn't matter, and only needs to be set explicitly if water hammer occurs.

 

[kevplumb]

you are in the proverbial so to speak
if the system aint filling you have a blockage on the cold feed usually where it joins the pipework

 

[Rab]

aye - i've drained the system again, and the cold feed isn't draining at all.

Is there a solution for this?

 

[bathjobby]

The new valves you've fitted to the radiators which now don't fill are OPEN aren't they ?

 

[kevplumb]

only realistic one is to cut the cold feed where it joins the system
i assume you have checked there are no valves in the line

 

[Rab]

aye the radiator valves are open, along with all the valves on the way to the radiators... but thanks for the sanity check

the pipes weren't filling up upstairs either as far as i could see. I tried bleeding the inverted pipe loops and they gave no sign of filling either.

I think it's down to the drain cock not working. It was a bit leaky anyway, and it turned out it was only letting water through if i opened it up and held the internal screw at a certain angle.

So I've re-drained the system, and fitted a new drain cock. I hope that once i get the system fully bled it will fix the cistern not feeding... that is if the problem is airlock.

 

[Rab]

Kevplumb (or anyone)... could you go into a little more detail about a cold feed blockage please?

It's looking like this well may be my problem, as although all the radiators are now full, the pump is running hot and noisy if i turn it on, and the boiler automatically switches off after a minute or two of starting up. (pilot stays alight, so it's not a flue problem).

So it sounds like there's no water there. The boiler could have a faulty stat I realise, but the hot pump suggests otherwise. Plus the fact that the CH refused to fill from the cold water feed, i guess all this would suggest that there is a blockage somewhere.

One thing I'm not sure about though, is that although the HW is coming out cold, all the hot water taps work, and the cold feed water level goes down and is refilled from the mains supply when the taps are opened. Are there two pipes from the cold feed, one for HW and one for CH?

...is it possible there's a blockage only on the CH cold feed, causing the boiler and pump to run dry?

 

[CH4]

In a close-coupled system, the cold feed is the 15mm pipe that connects the small header tank in your loft to the system. The 22mm pipe, which hooks over the top of the header tank, acts as a safety expansion pipe, and should connect to the system pipework within 150mm of cold feed.

Apart from when the system is filling, the flow through the cold feed pipe is usually very low - just that caused by water expansion and contraction (as the system heats up and cools down). Hence, it is prone to blocking.

If you can find a way to connect a hose to the 22mm expansion pipe, and your water mains pressure is high enough, you may be able to flush the blockage - by sending water down the expansion pipe and up the cold feed. If you empty the header tank first, and can reverse fill it this way, then at least you will know that the cold feed is not blocked.

This method of removing a blockage in the cold feed doesn't always work, even when a Powerflush pump is used. So you may have to do as kevplumb suggests, and cut out the blocked section of pipe and fit a new one.

NB Don't forget to bleed the pump when you refill the system.

 

[fronnie]

the gate valve is actually opening and closing isnt it fully in and out,ooeeerr sounds a bit rude, i went out to a call and the handle was only turning 3/4 a turn each way and the customer thought it was opening and shutting. The valve had scaled up and wasnt moving at all.
Just a thought for u to ponder

 

[Rab]

Cheers CH4. I'm going to try this out.

The pump thing, btw, was something that confused me a little... i thought that they were supposed to have a bleed screw, but on my model, a Potterton-Myson Compact, I couldn't see one anywhere.

 

[CH4]

The pump bleed screw is usually a large diameter flat disc in the middle of the motor housing, and it covers the end of the motor spindle.

 

[Rab]

Absolutely spot on CH4... i love you. my wife loves you. my cat loves you.
Thanks others as well

I had a look inside the feed & expansion cistern - it was totally gunged up with thick sludge and limescale. The cold feed outlet wasn't even visible under the solidified deposits. I removed the visible gunk fom the cold feed outlet, and shoved the garden hosepipe about a foot into the expansion pipe and turned it on full.

At first all the water came back through the expansion pipe, but after a few minutes bubbles started appearing from the cold feed pipe, until a load of sludge came out, a load of big bubbles, and then the water started flowing freely from the cold feed. I left the pipe on for half an hour with the cistern water running into the overflow, and cleaned out the cistern with a toilet brush.

When i turned the system back on i could hear it filling up immediately, and within minutes all the radiators started getting warm. I also bled the pump as directed... i had to remove the cylinder insulation jacket to find it. (they're right next to one another).

My only concern is that the bottom of the pump is very hot. I don't know if that's just heat from the hot water, or if I've damaged it by running the pump dry.

 

[htgeng]

I suggest you completely clean out the system next spring when the heating is not needed. use a chemical cleanser. might be worth replacing the pump when you have the opportunity as yours is probably on its last legs if system has been sludged up.

 

[Rab]

sounds like good advice ta. I'll have to do it in the spring anyway 'cos the missus told me I'm prohibited from any more plumbing until the weather warms up :/