Guest viewing limit reached
  • You have reached the maximum number of guest views allowed
  • Please register below to remove this limitation

Welcome to the forum. Although you can post in any forum, the USA forum is here in case of local regs or laws

View the thread, titled "Hot water demand effect on central heating for Combi boiler" which is posted in Boiler Advice Forum on UK Plumbers Forums.

M

MartinPod81

Hello,
We’ve recently moved into a fairly old, fairly big detached house (i.e. fairly draughty, but not too bad by any means) with a fairly new well maintained Worcester combi boiler. We weren’t convinced the heating was working right and then got hit with a £610 energy bill for the first 6 months! Anyway, after some investigation we have found:
The Central Heating “seems” to work fine. The CH water flow temperature can be viewed directly in the display. When the CH kicks in, you can see the boiler water temperature rise and feel the radiators gradually heating up. CH water temperature is set to 70degC on the boiler which it gets to and maintains and all the radiators get nice and hot and heat the house. I don’t have any experience with the rate at which the water is heated - it does seem to take a while but not so much that I think there’s a problem.
The issue comes when there is then a demand for hot water. As with any combi, priority is given to hot water so CH switches off. Once hot water demand ends, there is a pre-set delay in the boiler before the CH kicks in again. However during this period of hot water demand and delay, the CH water seems to lose a lot of heat. When the CH kicks in again, the water temp will be around 5 - 10 degrees less than where it was, it will rise by a couple of degrees and then actually fall by around another 5 degrees before starting to heat up again towards the set point. This seems like a big waste of energy, but ok for a one off hot water demand. But when there are multiple hot water demands over a period of time as with normal domestic use the CH can’t keep up when it kicks back in. It loses too much heat during the hot water/delay phase and takes too long to get back up to temperature that the CH water temperature never gets hot enough to get the radiators anything over luke warm before the next hot water demand cycle causes the CH temperature to reduce even further. Therefore the rooms never heat up but all the while the boiler is working away using energy/costing money.

We’ve had Worcester out and they say there is nothing wrong with the boiler and it’s working as it should, it’s just how this system is in our house. They also said they wouldn’t expect to see a combi boiler in a house our size partly for that reason.

Has anyone any thoughts or comments on this? It can’t be right that we can’t heat our home effectively without having to stop using the hot water. Hot water use isn’t large either, there are 3 of us and it’s just general hand washing, rinsing pots, wetting cloths for wiping surfaces etc.

Thank you
 
Hello,
We’ve recently moved into a fairly old, fairly big detached house (i.e. fairly draughty, but not too bad by any means) with a fairly new well maintained Worcester combi boiler. We weren’t convinced the heating was working right and then got hit with a £610 energy bill for the first 6 months! Anyway, after some investigation we have found:
The Central Heating “seems” to work fine. The CH water flow temperature can be viewed directly in the display. When the CH kicks in, you can see the boiler water temperature rise and feel the radiators gradually heating up. CH water temperature is set to 70degC on the boiler which it gets to and maintains and all the radiators get nice and hot and heat the house. I don’t have any experience with the rate at which the water is heated - it does seem to take a while but not so much that I think there’s a problem.
The issue comes when there is then a demand for hot water. As with any combi, priority is given to hot water so CH switches off. Once hot water demand ends, there is a pre-set delay in the boiler before the CH kicks in again. However during this period of hot water demand and delay, the CH water seems to lose a lot of heat. When the CH kicks in again, the water temp will be around 5 - 10 degrees less than where it was, it will rise by a couple of degrees and then actually fall by around another 5 degrees before starting to heat up again towards the set point. This seems like a big waste of energy, but ok for a one off hot water demand. But when there are multiple hot water demands over a period of time as with normal domestic use the CH can’t keep up when it kicks back in. It loses too much heat during the hot water/delay phase and takes too long to get back up to temperature that the CH water temperature never gets hot enough to get the radiators anything over luke warm before the next hot water demand cycle causes the CH temperature to reduce even further. Therefore the rooms never heat up but all the while the boiler is working away using energy/costing money.

We’ve had Worcester out and they say there is nothing wrong with the boiler and it’s working as it should, it’s just how this system is in our house. They also said they wouldn’t expect to see a combi boiler in a house our size partly for that reason.

Has anyone any thoughts or comments on this? It can’t be right that we can’t heat our home effectively without having to stop using the hot water. Hot water use isn’t large either, there are 3 of us and it’s just general hand washing, rinsing pots, wetting cloths for wiping surfaces etc.

Thank you
What's happening is just what you should expect.
Whilst the hot water is running the water in the rads is cooling. If you are running a bath heat could be off for quite a while. When the heating comes back on the return water will be relatively cold so the flow temp will drop for a few minutes. Just as when heating starts for first time it takes a while to reach specified temp.
 
Maybe the boiler has been range rated to a very low output, which doesn't affect its DHW performance, then, except that the DHW drawoff time is very long, say, if filling a bath or a very long shower, then the boiler (and rad) flow temperature should increase to its target level in a few minutes, the heat up time then depends on how low the room temperatures have fallen.
 

Official Sponsors of Plumbers Talk

Reply to the thread, titled "Hot water demand effect on central heating for Combi boiler" which is posted in Boiler Advice Forum on Plumbers Forums.

We recommend City Plumbing Supplies, BES, and Plumbing Superstore for all plumbing supplies.

Weekly or Monthly Email Digest

Back
Top