Microbore

[John]

I have just had my boiler replaced after 22 years of having a gravity fed C/H system I now have one that is mains pressure (filling loop / gauge). I have 2 radiators that have been sluggish and hoped that the higher pressure could improve the situation. It hasn't. Today I tried:

1. Close both radiator valves and open the drain c*ck in the valve to release residual pressure in the radiator.
2. Open lockshield on one end - got a full gush out of the drain c*ck. Closed it
3. Open TRV at other end - only get a trickle. Turned it on and off a few times - got some black particles out. Minor improvement maybe.

Any suggestions? Should I persevere weekly in the hope that if it is due to crud in the pipe it may eventually soften and get flushed out? Access the manifold and give the pipes a bit of a rattling about in the hope of loosening something?

The system did have a X800 cleaner in for about a week before the boiler was changed. It now has X100 in. Not sure when the problem started - it was certainly some years ago when I noticed it. I suppose it could even be a bruised pipes from the original build. The pipes are under chipboard floors so I can't easily change it.

Any tips or tricks?

[Spamlet]

If the TRV is like ours were, it will have a small steel pin in the middle that gets stuck down in the off position. You have to take the plastic shroud off the top and tap the pin to release it and open the valve. In my opinion this makes TRVs more trouble than they are worth and it is better to have an ordinary valve and turn it up and down manually if your room thermostat isn't good enough for you.

Another source of what seems to be 'sluggish' radiators is a three port mid position valve, that comes up in these columns time and again. These valves are designed to give the full power of the pump either to the hot water or to the CH, but they often get stuck in the mid position, where the supply to the radiators is not so effective. If your radiators were balanced with the valve fully in the CH only position, they may well not balance with the valve in the mid position, and you will experience this as some rads seeming sluggish in warming up. The valves are usually controlled by an actuator of a clever but failure prone combination of motor and microswitches. These actuators often fail and get stuck in the mid position, but can be replaced without having to change the valve itself, so you don't have to drain the system if you find it has stuck. You can tell if it is stuck by selecting CH only and then feeling the pipes that come out of the valve: if all three are hot, it's stuck. Occasionally the valve itself may get stuck, but usually it is the actuator.

S

[John]

It was sluggish with the old boiler and before I had TRVs. It is definitely the pipe. The flow from the pipe is poor (observed by opening the integral drain valve with one valve opened the other closed. Vice-versa and it gushes out.

[Spamlet]

Is this with the pump on or off? If it is not on then water may not be able to flow out of that section of pipe, especially if it is on a spur.

You should not be saying "it is definitely the pipe" but "why is water not coming from this particular pipe", and that depends on a number of other things:

If the TRV is on the input end of the rad and especially if this is a low point on the system, then that is where you would expect the sludge to collect in the pipe, but it rather depends on what is on the other end or the pipe; how much is horizontal and how much vertical, and, as I said, whether it is getting the full flow from the pump. If for example the pipe is 'T' d off another pipe, water will prefer to go straight across rather than round the corner, and the rads have to be balanced to offset this tendency, but even if they are balanced and your rad is often off or on a low flow, then that is where the crud will settle out. You may be able to blast it through by closing all the other rads, opening the sluggish one full on both sides, selecting CH only, and putting the pump on full speed. Repeat with all the other rads in turn, and this should at least redistribute any sludge. You then have to rebalance to get all the rads to the same temp via the lock shields, before putting the TRVs back to your preferred setting. (This can take some time and fiddling. Esp if your

3port valve or pump are not at their best.)

Seriously though: Did you check if you have a three port valve? because if you do and it is 22years old there is a good chance that is has not been working properly for a long time. You may also find that bleeding the pump helps.

If none of this helps, then you are looking at replacing that length of pipe, unless you can find some way of pulling a 'test-tube brush' through it. But as you say you have 2 sluggish radiators, I'd definitely look to your balancing and your valve before doing anything drastic.

S

[John]

The boiler is new. It is a pressurised system. Opening one end and the water gushes out. Opening the other end and it is a trickle. It has nothing to do with diverters or balance. Mains pressure will be more effective when one end is opened than any amount of circulating with a pump (circulator) The 8mm pipes are connected to a proper manifold.