Pipe size?

[shaggy]

This system belongs to a friend of mine who asked me why his heating isn't working. It's a Y plan and the mid-position valve isn't working leaving flow to cylinder only. It's not been done very well and you can see there is no access to the valve motor so I intend to reposition it. What I don't understand is why it's been installed with a restriction to the cylinder coil instead of 22mm. I don't do plumbing for a living so it's just a favour for a friend. Any suggestions?

 

[kevplumb]

for what its worth dont think it will make any diff

 

[PEDANTICVINDICTIVEMAN]

15mm feed to cylinder is fine, most likely the motor is nacked, as you say refit in a more maintenance friendly position.

 

[shaggy]

Kev, the opinion of a pro is worth something so thanks, and thanks for confirming that PVMan. I was thinking there was something I didn't know about pipe sizes, not being a pro myself and the installation was done by a corgi reg engineer. I think it is the motor as with ch 'on' there is power on white and with cylinder stat satisfied there is power on grey but it looks like the motor hasn't rotated to trip micro-switch as there is no power on orange. I can't get the cover off to get to motor as it is.

 

[CH4]

With a Y-plan, it usual to fit a gate valve (lock shield) between the 3-port valve and the cylinder coil, to balance the flows. The valve is adjusted, with the system in DHW only mode, by gradually closing it down until the boiler starts to become noisy (kettles), and then opening it up a little.

The constriction may be a cheapskate way of trying to achieve the same thing (the installer was probably trying to recoup the cost of the excessive amount of flux used).

 

[shaggy]

CH4, I've had a few houses with Y Plan but never seen that done. I was going to do it in 22mm. What about in summer when you only want dhw, if you've restricted the flow that much isn't the cylinder reheat time longer? I know what you mean about the flux. The heating engineer does live locally with a nice sign written van proudly displaying the corgi symbol etc. He may be qualified but he isn't a very good plumber. He extended the heating circuit in this property and he left the pipes to the new rads suspended by string from the rafters with gaps in the insulation. He also uses mostly end-feed and most of the solder is on the outside. I've already had to remake 3 joints that leaked. I'm pleased the heating is oil and not gas.

 

[CH4]

In the summer, the boiler's full output still goes to the hot water cylinder - at a reduced flow rate, but at a higher temperature (just below the kettling point). So the reheat time will not change. When the hot water and central heating are on together, you need to balance the proportion of heat that flows to the cylinder against that that flows to the radiators.

For example, if your boiler has an output of 15kW, then a good balance would be to send 3kW to the cylinder and 12kW to the radiators. Without balancing, the hot water would heat up rapidly, but at the expense of the central heating.

 

[PEDANTICVINDICTIVEMAN]

Average cylinder requires approxx 6 to 8000 btu's, as long as the boiler is getting correct flow through it to keep it happy 8mm pipe will heat the cylinder.

 

[shaggy]

Ok, so if 8mm pipes are adequate do we use 22mm because that allows for deposits in the pipe not to cause a problem as the internal dia reduces? When replacing cylinders I've seen the connecting 22mm pipes reduced to about 10mm internally just as they enter the cylinder.

 

[kevplumb]

so fit a high recovery cyl
pipework inside ( the coil) is only 8 mm

 

[shaggy]

I'm doing as little as possible on this job so I'm not changing the cylinder as it's a favour for a friend and there's no charge. In houses I've had with Y-plan, I've never noticed a problem with the cylinder taking more heat than the ch and none have had any restriction to control the flow to cylinder, they've all been on 22mm. The ones I've seen with deposits at the cylinder entry have probably run for years with no inhibitor so the large pipe size was a good thing. Thanks for info though.

 

[oilman]

.......I'm pleased the heating is oil and not gas.

Looking at the water pipes' joints doesn't give much confidence. Check there are no solder joints on the oil pipe. Get a new pipe fitted if there are.

 

[shaggy]

I'm not clear on that one oilman? What's wrong with a soldered joint on an oil line if it's done right? I've never had an oil boiler.

 

[oilman]

Solder melts in a fire and oil leaks out. It's prohibited under BS5410 which is the building regs approved document. Mechanical joints only permitted.

 

[shaggy]

Thanks, I didn't know that so I'll check it. (My next property may have oil ch as I have a diesel car).