Radiators not getting warm

[puffernutter]

I know, if it ain't broke.....

Over the summer, as part of a longer term task to fit a shower in the downstairs cloakroom, I made some minor changes to the central heating system.

In essence I needed the pipes to the radiator to come from the opposite side of the room and the only solution was to go "up and over".

I now find that the radiator, whilst full of water when bled, doesn't get hot. I wonder is this is because the additional load I am putting on my pump by requiring the water to go up 3m, then across the width of the room then down 3m. With the return doing the same.

When the pipework stayed on the skirting (as it was originally) the radiator worked fine.

If I remove the bleed screw, then the water will come through, albeit at a much lower pressure than I might have expected.

So, is the simple solution to fit a more powerful circulating pump?

Cheers

Peter

[Davey]

Not being a heating engineer, I would think that the net increase in length of pipework was part of the problem.

[Terry Fields]

At a rough guess, when you bled the radiator, one pipe (either feed or return) supplied the water; the other pipe still has a massive airlock in it. Terry Fields

[Toby]

I expect it is possible there is an air lock in this 'n' shaped pipe run.

I don't think the up/down is an issue, as you could setup a siphon with pipe as high as you like, as long as the outlet is below the inlet, it will work. The pipe resistance may well be an issue though.

I would try turning off all the radiators in the house, except this one, open the valves to this one fully, and then get the pump running, this may push any trapped air out.

Do you have a sealed system, or an open vented one?

[puffernutter]

All very good thoughts and advice. Thank you.

I will investigate and let you know what I find.

Cheers

Peter

[John Rumm]

Probably not. Its either an airlock in one of the pipes, or you need to rebalance the rads to allow for the extra flow resistance.

For an airlock, you will either need to find a way to bleed air at the top of the loop, or possibly just shut down all the other rads, and let the pump force flow through that problem one. That should shift the air (where will depend a little on the layout of the system and if its vented or sealed).

[Jeremy Nicoll - news posts]

It's hardly unusual for houses to have pipes that go up (from downstairs to upstairs) and back down again; I would have thought that pumps would be able to cope with that ok.

[chrisj.doran%proemail.co.uk]

I agree with others that the an airlock at the top of the n is a possibility. In a similar situation I know, with pipes going up 'n over a doorway at the highest point in the system, the Corgi (or whatever they're called this week) had to install what looks like an automatic relief valve to clobber the resultant perpetual airlock.

The other usual question following a summer shutdown is: has the TRV stuck? Remove the head and make sure that the pin moves up and down. You'll probably need a flat bit of metal to press against it. It should spring up and down a millimetre or so. If it doesn't, use pliers to work it up and down a few times, or a bit of "percussive maintenance" (tap it with a hammer) to free it. A new twist on this that I've recently discovered is that some TRVs (Landis & Gyr anyway) have a bias adjustment that you can use to set them, presumably so that 3 (say) is the optimum setting throughout the house. Somehow or other, some of these adjusters were keeping their rads off even with the head removed. It's a little clock-like thing with the "hand" slot you push round.

Chris

[dennis]

That's not actually true.. you can't exceed ~10m, at that point the water will break into a vacuum in the pipe and no water can ever pass using a siphon. Its the reason why wells have to have the pump at the bottom, you just can't "suck" water up any higher.

[Alan Braggins]

Not strictly true, but the OP's 3m is under that limit (about 34ft, 10.3m).

[charles]

Unless, of course, the pipes are filled with something other than water. If it were mercury, the allowable height would only be about 30 inches. ;-)

[Jules Richardson]

Agreed on the sucking aspect, but just to point out that a well doesn't have to have the pump at the bottom - mine's approx 86 feet deep with a surface-mounted jet pump (I'm not sure if there's a practical limit at which point a jet pump is no good and a submersible pump *has* to be used, however).

cheers

Jules

[Jules Richardson]

:-) How much mercury would you need to fill an average CH system? ;)

[hugh]

In CH systems pumps effectively don't push, they suck. If you run the pump with a bleed valve open you will simply suck in more air.

[The Natural Philosopher]

32 ft is as far as you can suck water up IIRC.

if your well is 86ft the pump is NOT at the top.

Unless its putting PRESSURE on the reservoir below.

So I guess the pump mechanicals may be a ground level, but the actual jet part is way down where the sun don't shine.

[The Natural Philosopher]

wrong, as usual. They essentially do both.

The correct way to get out trapped air is to run the pump flat out with plenty of pressure in the loop, and shut down everything except the cold rad. WITH LUCK this will blast the air to a lower point where it can be bled.

In my case a high loop through the attic was the issue..eventually it blew the air down into a bleedable rad.

[Alan Braggins]

"several hundred feet". But part of the pump mechanism is down the well even if the main pump is on the surface, you can't suck it up from above that far.

[Jules Richardson]

Yes, it is. It's an injector-type setup; on the surface is a large centrifugal pump which diverts a portion of the pumped water back via a return line down to the jet at the bottom of the well - e.g. see under "well pumps":

suppose you could term the jet to be a "pump" too, but to me it's just an injector and the actual "pumping" is all done top-side.

I don't think they're as common these days (submersible pumps are the norm), but I like them because just about all of the critical stuff is at surface level so can be worked on easily.

Looking at the manual for ours, 150 feet seems to be the depth limit, but I don't know if that's a technological limit or specific to the pump / jet that we have - that and ours turned 40 this year, so maybe things have moved on since then :-)

cheers

Jules

[The Natural Philosopher]

well exactly.

as long as you have pressure at depth, you can in pronciple pump to any height.

The 'working' part of a jet pump is the jet.

That's at the well bottom.

[Andy Webber]

Just to be sure ... the valves at both ends of the radiator are open, aren't they?