Central Heating Only Coping With Heating 3 or 4 radiators

[oldbutnotdead]

It'll be worth giving the X400 another week.
Do you have any tanks in the loft? An open vent setup will usually have 2 - one large header tank for hot water (150 litres or so), one smaller f & e tank for the boiler (20 litres or so).
What diameter are the pipes feeding the radiators? Ground floor rads- do the pipes come up out of the floor or down from the ceiling?
Flushing radiators is an easy (potentially messy) DIY job. Before doing that I'd be checking the flow and pressure at one or more rads (plenty of polythene on the floor and up the wall behind the rad, turn both valves off, loosen and release one valve from radiator, catch the water in a bowl. Once 1 end is dry, do the other end. Then finally with the bowl under one end of the rad, lift the other end.
The water shouldn't be too mucky (given recent powerflush and x400 dosing).
If you have a couple of bungs the right size, stuff them in the radiator ends and take it outside.
Back to your internal pipes. Bucket or bowl at one valve, turn it on. Water should flow freely and quickly.
Repeat with the valve at the other end.
Back outside to your radiator. Sit it correct way up to start with at a slight fall.
Hosepipe in the high end, turn tap on full.
Water should come out the other end, it shouldn't 'back up' within the rad. If the water is black or mucky, keep flushing til it runs clear. Start hitting the rad with a soft mallet, see if more crud starts coming out.
Finally set rad upside down, flush, keep hitting it.

 

[fixitflav]

yes, it's on 4 (out of 5)

But is it working properly? I don't suppose you can check it, but your plumber should be able to. If it's cutting out too early it might account for your symptoms. Does the flow pipe from the boiler get really hot?

Yes, controlling HW from the Potterton programmer

But what system? Do you have a 3-port valve (W or Y-plan) or two 2-port valves (S-plan) or none of the above, or something else?

Is it fully-pumped? Gravity HW unusual these days, but possible with this boiler, extract from manual below

To ensure optimum boiler performance on both gravity hot water
and fully pumped systems a change-over switch is incorporated in
the boiler control box. The boiler is supplied with the switch set for
sealed or open vented fully pumped systems.
If the boiler is to be used on a system with gravity hot water the
switch should be set at the GRAVITY position. In addition the bulb
of the overheat thermostat should be repositioned as shown in
FIG. 21

 

[altsaint]

What is the boiler size, is it a 30 40,50,60 or 80E, it will be labelled somewhere.

There's a label that says 'Potterton Profile 80 NG". Does that help identify it?

 

[altsaint]

Some more answers (or non-answers):

Do you have any tanks in the loft? An open vent setup will usually have 2 - one large header tank for hot water (150 litres or so), one smaller f & e tank for the boiler (20 litres or so).

In the loft, there are only 2 tanks - one for cold water, and the other (about 20 litres) which I believe to be the central heating expansion tank.

What diameter are the pipes feeding the radiators?

Using a ruler, I'd say a bit less than 20mm - maybe 18mm? There is one small rad fed by microbore for some unknown reason.

Ground floor rads- do the pipes come up out of the floor or down from the ceiling?

Pipes come out horizontally from the walls - I don't know which way they turn behind the walls

Does the flow pipe from the boiler get really hot?

Yes. And the hot water is hot. And most of the rads are hot individually (i.e. when I turn off most of the remainder)

But what system? Do you have a 3-port valve (W or Y-plan) or two 2-port valves (S-plan) or none of the above, or something else?

Is it fully-pumped?

Those questions I can't answer.

 

[fixitflav]

Yes. And the hot water is hot. And most of the rads are hot individually (i.e. when I turn off most of the remainder)

OK, that pretty much rules out my theory about the control-stat!

 

[Johntheo5]

There's a label that says 'Potterton Profile 80 NG". Does that help identify it?

Yes, thats a 23.45kw boiler which has ample power.

Next time the CH is on have a look into the small (feed&expansion) tank in the attic and check for any water coming out of the (bent over) vent pipe or any movement in the tank.

If you have a 3 port valve, a valve with 3 pipes connected to it then you will have a fully pumped system, if a 2 port valve (or valves) then possibly a gravity HW system, another way to check for a gravity HW system is to put the HW only on, the boiler will run but the circulation pump will not.

3 Port Valve

2 Port Valve

 

[oldbutnotdead]

OK.
Follow the advice about looking in the loft when ch or dhw are calling for heat. Some pics of pipework coming out of and around the boiler and the hot water cylinder would help to determine how your system is set up.
I suspect you'll have to either get your hands wet/dirty or pay someone else. Suggest in the latter case you ask the plumber to start by dropping one rad off and checking flow through the pipes to start with (rather than going straight for blocked rads being the solution).
You might also want to invest in a magnet and run it over any elbows, tees etc near the boiler and hot water cylinder (looking for magnetite buildup).
EDIT Plumber may be suggesting blocked rads because flushing rads is an easy time-consuming profitable job. Rectifying blocked pipes in a finished house can be a total nightmare- moving furniture, lifting carpets.

 

[altsaint]

Next time the CH is on have a look into the small (feed&expansion) tank in the attic and check for any water coming out of the (bent over) vent pipe or any movement in the tank.

I did that, and no water emerging from the vent pipe and the tank is still

I can see two valves like the 2 port one you posted, near the HW cylinder and pump.

another way to check for a gravity HW system is to put the HW only on, the boiler will run but the circulation pump will not

Interesting! I did this and 1) the pump came on but not the boiler, and 2) It took nearly 10 mins for the boiler to kick in. The water hasn't been heated for over 6 hours and during that time a bucket of hot water has been used. So surely the boiler should have come on as soon as I switched it on the programmer?

 

[altsaint]

Plumber may be suggesting blocked rads because flushing rads is an easy time-consuming profitable job. Rectifying blocked pipes in a finished house can be a total nightmare- moving furniture, lifting carpets.

Plumber B had good reviews and worked hard to fix the problem, but it was all trial-and-error with no firm diagnosis. I don't know him that well, so your observation could still be correct. Plus if not the rads, then the problem will still be there at the end! Plumber A has been technically accurate with his work over the years, but I know he doesn't like difficult jobs. Which I think is why he's not returning my calls.

 

[oldbutnotdead]

Hopefully at least one of the plumbers has checked that the motorised valves are working (powerflush boy should have latched them open) but do check yourself.
If they are Honeywell valves there's a small metal lever on one end of the housing. Push that lever sideways- if the valve is closed you should feel some resistance, if it is open the lever should move very freely. Also, when the boiler/heating is running check pipe temperature both sides of the valves- with valve open temperature should be near enough identical

 

[Johntheo5]

I did that, and no water emerging from the vent pipe and the tank is still

I can see two valves like the 2 port one you posted, near the HW cylinder and pump.

Interesting! I did this and 1) the pump came on but not the boiler, and 2) It took nearly 10 mins for the boiler to kick in. The water hasn't been heated for over 6 hours and during that time a bucket of hot water has been used. So surely the boiler should have come on as soon as I switched it on the programmer?

The pump starting up means that the cylinder stat was calling for heat, the 2 port valve probably did open as this gives the signal to the boiler and pump to run but the boiler wont fire until its own thermostat is calling for heat so yes strange that it took 10 minutes, if the boiler had just been running previously then you might expect a few minutes for its temperature to drop.
A few other easy items to check out, check that the arrow on the side of the pump body is pointing towards those 2 port valves and check that the pump is set to speed 3.

 

[altsaint]

A few other easy items to check out, check that the arrow on the side of the pump body is pointing towards those 2 port valves and check that the pump is set to speed 3.

The pump is set on speed 3, but I can't see an arrow on the side of the pump body, perhaps because it's on the side I am unable to view

 

[Johntheo5]

If the 2 port valves are on the pipe above the pump then more than likely pump pumping upwards, correctly.

 

[altsaint]

If the 2 port valves are on the pipe above the pump then more than likely pump pumping upwards, correctly.

Hmm. They're actually on a pipe that tees off the down pipe. This was one of my concerns with the plumber fitting it, as it took him a couple of tries to get it 'fitted correctly', and he didn't seem totally confident with this particular task. Also, I don't think I mentioned earlier, but the new pump has a variably noisy hum, and occasional clunking from the area where the pump is installed.

But if it was installed incorrectly wouldn't it be the case I'd get no output at all?

 

[Johntheo5]

Beg, borrow or steal a mirror so you can extablish 100% which way that pump is pumping, presuming that the pump is on the boiler flow then IMO wrong IF pumping upwards, you will have to establish that as it may be pumping correctly downwards and the plumber just turned the pump head through 180 deg.