Major system problems - BG stumped.- SOLVED

[mattymoo]

My system is mains gas, Netaheat Profile 60e with 10 rads, 4 upstairs and 6 down.

I have a BG 3 star maintenance plan.

Events go like this:-
System functioning okay bar one rad downstairs. Boiler keeps tripping out on overheat though.
BG do annual visit 5/1/06. Diagnose problem with TRV on rad and pipe connected to fan sensor is disconnected. Replace pipe. System okay now but not brilliant. Engineer also strongly recommended powerflush for £440.

11/1/06 - reset switch on boiler fails completely. Engineer visits and orders part.

13/1/06 - part fitted but in meantime all bar one of the downstairs rads is failing to heat. Flow pipe is hot but return pipe is cold. Upstairs is fine. Header tank filling with hot water. He replaces the following:-
2 Ranco thermostats.
Grundfoss main circulation pump.
2 x 22mm pump valve ball type.

I agree to have the powerflush done and engineer asks for a rush job. This is a friday. Call received saying powerflush will be done monday 16th.

16/1 - powerflush started at 9:30, engineer leaves 4:30. System is in a bad way and he will have to come back. Blockage somewhere. No heat or water. Engineer has flushed all rads and the primary circuit. Powerflush machine connected across downstairs radiator tails.

18/1 (today). Engineer returns at 9:30 and leaves at 3pm. Primary system re-flushed. Downstairs rads removed and flushed through by hose. This time he flushed across the primary pump.

End result - upstairs rads are super hot. Downstairs rads bar one are stone cold. The one rad that is working is a more recent addition to the system and is branched off the main pipes at ceiling level.

The system has been flushed twice now and I cannot fault the guy, he was very thorough. He says he will need to return next tuesday at the earliest and either
a) re-flush for a third time.
b) investigate possible system design fault with floorboards up etc.

Does b sound likely? System is around 15 yrs old and has worked perfectly up until the start of this year. All rads were uniformly hot.

Is it possible one of the engs has done something inadvertantly that is stopping the flow to the downstairs rads? I asked if the motorised valves were set okay - he said yes. (had a problem with a motorised valve a few years back that gave similar symptoms).

Any ideas?

 

[ChrisRoberts]

"440 for a powerflush! Is that each one?

 

[mattymoo]

£440 for the powerflush. All in price for as long as the job takes as I understand it.

 

[ChrisR]

Blockages in heating systems, which a powerflush will hardly touch, are not rare. Even if the machine is applied directly across the blockage, there may still be little or no flow. If there is no flow then the machine has no effect.
If the rads are on "drops" of pipes down to each one, imagine the effect of a handful of rust at the lower end of the pipes. If any other path is open, there wil be almost nothing going through the obstruction. Connecting the machine at each radiator in turn MAY clear it.
If you tip the best descaling chems onto a bucket of rust, only some of it dissolves.

 

[Agile]

I do have to say that they have not skimpted on the time spent on the job.

Perhaps there is some lack of skill?

Obviously your description may not totally relate to the technical facts.

In reality the solution may be something as simple as balancing of the rads.

Power flushing a sludged system can alter the balance as dirt is removed and differential flow resistances altered.

My suggestions would be a balance related investigation of the flow characteristics.

Tony Glazier

 

[kevplumb]

wah
wah
wah

 

[meldrew's_mate]

Do you have two 2 port valves?

Check the heating valve opens fully, and the hot water valve shuts when not required.
Check the new pump is not blocked with dislodged debris.
Turn the upstairs rads off and the pump speed to max (3). Does this improve the downstairs rads?

There is certainly a clear indication of lack of flow, this is where BG should be concentrating, and they should connect the powerflush pump across the pump connections and flush each rad in turn by isolating all but the one to be flushed (and so on ...).Don't forget to treat the DHW cylinder as a rad for this purpose, and turn off any fixed bypass valve.

Finally I suggest the installation of an auto-bypass valve as the boiler needs the pump to run for a couple of minutes after the burner goes off, and needs water flow to disperse heat. The pump should be powered from the boiler's pump output to achieve this.

 

[mattymoo]

Do you have two 2 port valves?

Check the heating valve opens fully, and the hot water valve shuts when not required.
Check the new pump is not blocked with dislodged debris.
Turn the upstairs rads off and the pump speed to max (3). Does this improve the downstairs rads?

There is certainly a clear indication of lack of flow, this is where BG should be concentrating, and they should connect the powerflush pump across the pump connections and flush each rad in turn by isolating all but the one to be flushed (and so on ...).Don't forget to treat the DHW cylinder as a rad for this purpose, and turn off any fixed bypass valve.

Finally I suggest the installation of an auto-bypass valve as the boiler needs the pump to run for a couple of minutes after the burner goes off, and needs water flow to disperse heat. The pump should be powered from the boiler's pump output to achieve this.

2 port valves - are these the Honeywell motorised valves? If so then yes, system has 2.

Downstairs rads will heat if upstairs are turned off.

Rads were flushed with the powerflush connected across the tails of one of the downstairs rads. Each rad isolated in turn.
Primary circuit (as BG described it but guess he means flow and return) flushed with machine connected across the circ pump area. When he realised downstairs rads were not heating he removed them and manually flushed them.

Had a look tonight. With upstairs rads on the main feed pipe (descending from pump on 1st floor) is hot. Then goes under floor and onto 1st rad in living room. Feed up to TRV is hot but rad is cold. Checked the TRV and pin is working okay.

This radiator has been flushed twice so what is stopping it working?

PS: Thx everyone for the help so far.

 

[DP]

Cannot see why anyone should be stumped with this type of problem (a pro that is)

I would shut all the rads except two. Of the two one should be the rad that fails to heat and anopther downstream or upstream of aforementioned rad. Run the boiler and carry out a flow and return temperature check on these two rads.

I would expect a temperature difference of 11 to 20 degrees C on both. If the cold rad still fails to heat, I would check the pipe that connects this rad to the flow and return. It will either be blocked, (with plastic very likely) or airlocked.

 

[mattymoo]

UPDATE
BG visited again last week and flushed the system for a third time. That took up the morning.
The engineer then spent the afternoon balancing the system. He discovered the bathroom rad was the key to the system. The system is not "commoned" correctly and if the bathroom rad valves are fully open, water does not flow to the downstairs rad. By fully closing them and then opening up a couple of mm the system works correctly.

Credit to BG. This cost me £440 and endless cups of tea for the engineer. If I had paid a plumber for 3 days work it would have cost in the region of £1200 to £1500. I also have a new pump and new gate valves all free of charge.

 

[ChrisR]

if the bathroom rad valves are fully open, water does not flow to the downstairs rad

That isn't uncommon at all, but when it's just one of a number of "features", things can take a long time to sort out. Glad you got there in the end and thanks for coming back.

 

[chrishutt]

The engineer then spent the afternoon balancing the system. He discovered the bathroom rad was the key to the system. The system is not "commoned" correctly and if the bathroom rad valves are fully open, water does not flow to the downstairs rad. By fully closing them and then opening up a couple of mm the system works correctly.

As ChrisR said, the need to balance the flow through each rad (especially bathroom rads) by adjusting the lockshield rad valves has been standard practice for decades, yet your "engineer" has only just "discovered" it. The bit about the bathroom rad being "the key" and not being "commoned correctly" sounds like nonsense.

 

[mattymoo]

I understand what you are saying but I cannot fault the guy. To me, the end consumer, he appeared competent and conscientous.

Out of interest though - why bathroom rads especially?

Key was my word btw but he did say "not commoned correctly".

 

[chrishutt]

why bathroom rads especially?

Firstly because bathroom rads usually have low heat outputs compared to other rads (bathrooms being small) and so require less through flow of heating water.

Secondly bathrooms are often close to where the pump is located (e.g. airing cupboard) and so the pipe runs are often much shorter than for other rads. Water tends to take the easiest route from A (pump) to B (common return pipe) and so this requires even more restriction of through flow.

 

[DP]

Do not forget the cost of powerfluhes.

When the rads do not heat up correctly, easiest way of coming to a resonable conclusion is to touch the flow and return pipes at each radiator. One does not needs extra brains to do this, (or powerflushes) only an unerstanding of water flow and its effects.