combi water temps

[gazz]

dunno if this is normal or not......

got a combi unit, halstead gold something or other, we have both temp dials on the front panel up on max.

the central heating is now controlled by a wireless thermostat, hence why i have the heating temp at max... so the wireless stat controlles the turn off temp and not the boiler, the time switch is just turned to on all the time.

when the heating is not on, if we open a hot tap, it takes about a 20 seconds to get hot water, and it will get steaming hot.

however when the heating is on, opening a hot tap results in lukewarm water, no matter how long we run the hot tap for, tried having the tap barely open, fully open and all positions inbetween, we only get luke warm water.

is it normal to get lower temp hot water when the heating is on on a combi? im thinking that when heating is not on, the boiler can heat the hot water as hot as it likes, but with heating on if it tried the same it'd overheat the heating water circuit.

[BigWallop]

Turn the Boiler Thermostats, both of them, down to around two thirds of the dial. At maximum, the water is being heated way past what your system is demanding from it. At a lower output on the boiler, the system will demand only what the boiler can give.

[NOSPAMnet]

Especially the DHW thermo. That should be set to a comfortable temp to avoid scalding

[gazz]

okiedokie, it was a plumber who told me to keep them both at max, but aid to turn all the rad valves to 3/4 open to reduce fuel usage (have normal rad valves, not thermostatic ones)

he also said no point balancing our system as we have a mix of 15mm and 8mm pipe in the system, (2 rads are fed with 8mm, the rest in 15mm)

[BigWallop]

Personally, I'd have said the valves on the wider bore feed pipes would best at half closed / open and the narrow feed pipework should have been full open. But that's just me. I don't know exactly how your system is designed.

Do you notice any significant difference in the heating time of the radiators? With a good balance to the system, your radiators should all begin to heat up at the same time. Not the pipework. The radiators. If they don't, then a bit of balancing out might be a good idea. It takes a bit of patience and time, but it is worth the effort.

You have to remember that your plumber just wants the system to work without leaks or cold spots, but they won't take time to go around and properly balance everything out. That's best done by yourself anyway. You're the one living with it.

[John Rumm]

In a word, no.

Sounds like it may be the diversion valve not doing its stuff.

The water heating will usually take total priority over the central heating. So the heating being on or not ought to make little difference. You may get a slight difference in initial temperature of DHW with the CH on, but once the water has run for a little while and the temperature stabilised its temperature should be limited wither by the DHW stat[1], or the ability of the boiler to heat it fast enough.

[1] What happens when the water exceeds the limit set on the DHW stat will depend on the type of boiler. A fixed output one will cycle the burner on and off, more modern ones will modulate the input power down to match the demand first if possible.

[Dave Liquorice]

I'd have said having a mix of pipe work and all manual valves would really demand a proper balance of the system as those on the smaller pipes won't be getting the same flow as the ones on larger. It does depend entirely on the topography of the system though. Wander over to the FAQ and checkout the bit of balancing it's easy to do and worth it

Moral, don't believe what plumbers tell you, they just want to whack the system in and have it work acceptably well for the first time it's fired up. It does take a while to balance a system properly the plumber would rather be off doing something else than waiting for the system to stabilise after each adjustment...

[dennis]

He may have been a plumber but he knows sod all about heating systems.

If you have high resistance paths (8 mm) and low resistance paths (15 mm) it needs balancing more.

Don't bother doing the balancing until you fit TVRs and you can do it once rather than twice, assuming you are doing so soon.