Central heating pump isolation valves won't seal

[Simon]

Hello -

I recently tried replacing my noisy central heating pump. To my surpise, the isolation valves on either side weren't seized, and they seemed to turn smoothly through several revolutions as I closed them. Unfortunately when I started unscrewing the 2 large nuts securing the pump, water started flowing out quite quickly. It's not easy remembering which way is clockwise when you're lying underneath an immersion heater being sprayed with warm dirty central heating water, wondering how long it will take for the water to reach the nearest lighting junction box.

Any guesses on what went wrong? Are the valves likely to be silted up? The system probably hasn't been flushed for a long time.

I'm hoping that the rapid outflow that occured during my last attempt might have cleaned the valves sufficiently for another attempt to be worthwhile. Or should I just give-in, drain the system and replace the valves? Is fitting a new pump without flushing a possibly silted-up system false enconomy anyway?

FWIW, the valves are similar to this:

the pump is similar to this:

[Vortex]

[Simon]

There's a small tank with a ball-valve in the loft next to the main cold water tank, which has a lift-off lid, so I guess it's not sealed. The tank is about 3 metres above the pump, so there's not an enormous amount of head at the pump.

I've bought a spare valve to play with, and it's difficult to see how it could fail to seal, unless it's severely corroded or silt prevents a seal from being formed.

[Andy Hall]

These are usually gate valves and don't work terribly well at the best of times. Any crud would tend to result in leaks.

The system shouldn't have accumulated much silt if it has been properly and regularly dosed with corrosion inhibitor.

One can always hope. Here the mess involved, the likelihood of a poor outcome and the low cost of fixing don't make it worth hoping.

Yes on all counts.

Then either side of the pump, I fit a lever ball valve (e.g. Screwfix 17293). These seal properly and don't stick. Very cheap and available at B&Q on Sundays.

The system should be drained and properly flushed. I do this by removing the radiators one at a time, taking them outside and flushing through with a pressure washer. At each radiator position, I flush the pipework from each valve. Care because sludge and CH water stains indellibly.

However, you may not wish to undertake this at current temperatures a week before Christmas. In that case, I would flush as best you can and add a cheap inhibitor such as Screwfix 94270 to at least prevent further damage and then do the flushing job in the spring using a sludge remover after flushing and then finally filling with a good quality inhibitor such as Fernox or Sentinel.

[Rick Hughes]

It is fairly common for these valves to fail to isolate when they have been in place for a long time - the silt, crud & corrosion build up stops them closing down fully on the seat - doesn't take much to stop a good seal.

Get the system hot - drain it, refill and add a flushing additive, again get hot and drain, fill once more with clean water to flush out ... change your pump & valves, then refill with correct inhibitor.

Interesting the CORGI guy who issues the saftey cert on my boiler never installs inhibitor - claims it is a waste of money. I alwasy use it though.

>

[Andy Hall]

I wonder why.

- £20 cost to protect £5k investment.

- Don't spend £20 of the customer's money - £5k business opportunity in a few years time.

A wise investment. I've used it in various systems for 30 years, renewing annually - never anything more than a few grains of silt - mostly plumbing swarf and never anything replaced through corrosion. No £5k business opportunity either.

[David Hansen]

On Sun, 17 Dec 2006 08:47:14 -0000 someone who may be "Simon" wrote this:-

Pump valves often fail, as people tend not to operate them every six months or so to keep them working. A drain down, new valves and new lot of chemicals tends to be the solution.

[The Medway Handyman]

[dom]

Have to agree. They can "influence flow rate", maybe a brand new one could (more or less) stop a low pressure flow.

[Andy Hall]

Which makes one wonder why they are fitted at all.

[John Stumbles]

Plug the outlet of the tank and the vent pipe and open the pump union slowly with a container underneath. The water should stop when it develops a partial vacuum due to the blocked tank connectoins and you can work on the pump relatively dryly.

The ball-type (with a screwdriver slot) are more likely to close properly if they're not completely siezed but all types are likely to be a chocolate teapot by the time the pump needs replacement.

[Dave Plowman (News)]

Fact of life with gate valves, unfortunately. Especially in a hard water area.

[Pete C]

Are the gate valves horizontal?

Best to close each one momentarily while the pump is running, the flow while the valve is closing will help flush any silt accumulated in the bottom of the valve.

cheers, Pete.

[Pete C]

Also try tapping the bottom of the valve while the valve is partly closed and the pump is running, it might help dislodge any crud stuck in the guide of the valve.

cheers, Pete.

[Dave Plowman (News)]

It's a waste of *his* money and bad for repeat business. Besides, a system without it will probably survive any warranty period. But when you read all the tales about blocked systems and 300 quid power flushes being needed I'm glad I've spent *my* money on inhibitor.

[Osprey]

aid:

Could understand your scepticism - but he is a family friend - charges me zero for annual safety check & certification. I installed the system myself - and he knows that I would fix anything myself - so he has nothing to gain financially from this advice - which I don't follow.

[Andy Hall]

That's OK then. It's just rather surprising that he would find inhibitor a waste of money given what happens if it isn't used.