Using Heating and Hot Water at the same time

ImranQ

Ectophile said:

It may come down to the controller, the 3 port valve and/or the thermostats (room and tank).

My central heating can be set to heating and water at the same time, but I don't bother, as the controller gets confused by two thermostats if one calls for heat and the other doesn't.

Thanks that is useful to know. 

lohr500

ProDave said:

Verdigris said:

Installations vary, but usually the boiler only satisfies one load at a time. Mine always satisfies hot-water first, so the heating doesn't come on, first thing, for about 10 minutes, until the hot water tank is up to temperature.

No a gas boiler is well capable of doing hot water AND heating at the same time.

If it worked with the old tank as you expect and does not work properly with the new tank, the installer has messed something up.  Plumbers are not usually electricians and it is amazing how many times they try and do something like that and mess it up.

Agree with ProDave. If it all worked OK before changing the tank and it doesn't now then it would suggest the engineer has messed something up.

When you say "pressure tank", what do you mean? The large immersion tank that holds the hot water or a smaller pressure vessel that forms part of a system boiler set up.

ImranQ

lohr500 said:

ProDave said:

Verdigris said:

Installations vary, but usually the boiler only satisfies one load at a time. Mine always satisfies hot-water first, so the heating doesn't come on, first thing, for about 10 minutes, until the hot water tank is up to temperature.

No a gas boiler is well capable of doing hot water AND heating at the same time.

If it worked with the old tank as you expect and does not work properly with the new tank, the installer has messed something up.  Plumbers are not usually electricians and it is amazing how many times they try and do something like that and mess it up.

Agree with ProDave. If it all worked OK before changing the tank and it doesn't now then it would suggest the engineer has messed something up.

When you say "pressure tank", what do you mean? The large immersion tank that holds the hot water or a smaller pressure vessel that forms part of a system boiler set up.

The large immersion tank I believe. This was the cylinder that was installed:
https://www.screwfix.com/p/rm-cylinders-stelflow-indirect-unvented-cylinder-250ltr/32745

ImranQ

Verdigris said:

Installations vary, but usually the boiler only satisfies one load at a time. Mine always satisfies hot-water first, so the heating doesn't come on, first thing, for about 10 minutes, until the hot water tank is up to temperature.

Where is this prioritisation change made?

Reed_Richards

ImranQ said:

We have a Nest programmer and using the manual On/OFF.

Your may have a valve arrangement that enables you to heat the radiators and your hot water simultaneously.   Or it may be one or the other.  Whatever programmer you have needs to know which it is (and be wired so that it can operate the valves correctly).  

jrawle

It could be an issue with the balancing. Just as radiators are balanced against each other so that they all get hot at the same time, the hot water loop should also be balanced against the central heating. If the plumber really didn't touch any of the wiring, then the balancing seems to be the most likely culprit because he has changed the pipework to the tank and/or the setting of any balancing valves. If the valve is not open enough, most water will flow through the radiators instead of the hot water tank. If the radiators are off, then the water does go through the tank and heats the water.

Otherwise, as the other posters have said, it could be a failed valve. The plumber may have disturbed the wiring, or it could be a coincidence. You could check that the valves operate as expected as you switch between heating, hot water and both. Exactly what valves do what will depend on the setup you have: usually one valve that has three positions, or two valves that each have two positions. Nest should make this easy as you can sit in front of the airing cupboard with your phone and see what the valves do as you switch things on and off.

As for the banging, as it's an unvented cylinder, presumably there is no header tank, so it is fed from the mains. Perhaps the stop-tap has been turned on more than is was before so that the pressure is too high. Try turning it down. Otherwise, it could just be that the new pipework is looser so that it moves about more, or if you are in a hard water area, you may get more flow as it is no longer scaled up.

Reed_Richards

ImranQ said:

We have a Nest programmer and using the manual On/OFF.

If the Heating is ON, and the house has warmed up and we simultaneously turn the Hot Water ON in the Nest programmer the display says the Hot Water is ON as well as the Heating. But the water barely gets luke warm even after the Hot Water is on for 1/2hr or 1hr.

If you have a programmer you really ought to use it properly, not just as an on/off switch.  So if you turn your heating off at night then program the hot water to be on for an hour before your heating starts in the morning (or you switch it on, if you must).  That way you will have a tank of hot water waiting which may well last you the rest of the day.

If you ask for heating and hot water at the same time and your valve arrangement can only give you one or the other then  your programmer has to decide which to choose.  Normally the priority is given to your hot water and the heating will go off whilst the hot water tank is being heated.  But your programmer may give you the option of giving heating priority in which case your hot water will never come on until the Nest room thermostat reaches the temperature that it is set to.  if you are just using  your Nest as an on/off switch that may never happen.   

ImranQ

Reed_Richards said:

ImranQ said:

We have a Nest programmer and using the manual On/OFF.

If the Heating is ON, and the house has warmed up and we simultaneously turn the Hot Water ON in the Nest programmer the display says the Hot Water is ON as well as the Heating. But the water barely gets luke warm even after the Hot Water is on for 1/2hr or 1hr.

If you have a programmer you really ought to use it properly, not just as an on/off switch.  So if you turn your heating off at night then program the hot water to be on for an hour before your heating starts in the morning (or you switch it on, if you must).  That way you will have a tank of hot water waiting which may well last you the rest of the day.

If you ask for heating and hot water at the same time and your valve arrangement can only give you one or the other then  your programmer has to decide which to choose.  Normally the priority is given to your hot water and the heating will go off whilst the hot water tank is being heated.  But your programmer may give you the option of giving heating priority in which case your hot water will never come on until the Nest room thermostat reaches the temperature that it is set to.  if you are just using  your Nest as an on/off switch that may never happen.   

Yes I agree. Actually, that is what we usually do. Sometimes however, if there is excessive water use in the day then we may need to turn it on in the day. I will check the settings tomorrow. Many thanks!

Reed_Richards

These Nest instructions might help: https://support.google.com/googlenest/answer/9259578 .  They seem to indicate that you need to "Boost" your hot water if you want to heat up the tank.

ImranQ

Reed_Richards said:

These Nest instructions might help: https://support.google.com/googlenest/answer/9259578 .  They seem to indicate that you need to "Boost" your hot water if you want to heat up the tank.

We have a Nest schedule to turn on the Hot Water in the morning before everyone wakes up. Then we use the 30-60min Hot Water boost during the daytime, as needed. When I said manually, I was referring to the boost. This is where the problem happens that when the boost is turned on at the same time as the heating, it doesnt seem to work. If the heating is OFF, then the Hot Water works as expected.