Abrupt Pump Shut Down

[WarmBumble]

Long time follower - first time question
I have installed an Evohome system to replace a standard BG installed Y plan single thermostat system and having read many of the threads on this forum appear to have avoided many of the problems others have experienced and sought answers to through here. I have however pne apparent problem, when the central heating reaches the locally set temp there is a what appears to be an abrupt shut down I.e. there is a bang which can he heard through the pipework. Feels like the pump is being stopped abruptly. Any ideas if this is something which can be avoided through any setting? When I originally setup the system with CH only (no HW control) I think there was a pump overrun setting for the boiler control, but with the the HW control added there is no longer that setting.

The system comprises an evohome based controller, the hot-water pack, 12 HR92s contolling 11 different rooms, and 2 bathrooms with the original TRVs left on so they come on whenever some part of the house is being heated. To keep the wiring simple and avoid undoing what is already there, I used the terminations from the old programmer to feed the BDR91s I.e. Live and Neutral feed both BDR91's and the CH on feeds the Heating BDR91 and the HW on and HW off feed the HW BDR91. The old thermostat is then left high (i.e. always on) and the odl HW tank thermostat remains in the airing cupboard but will not reach HW temp and so is always calling for heat when asked by the Evohome. This was primarily to allow me to go back to the old system if I wanted.

Any thoughts anyone?

Were it not for the shutdown noise, I'd say it was the best system I've come across, so flexible and even the wife thinks it's a brilliant gadget.

P.S. The knowledge sharing though this forum has been an exceptional help

[top brake]

Long time follower - first time question
I have installed an Evohome system to replace a standard BG installed Y plan single thermostat system and having read many of the threads on this forum appear to have avoided many of the problems others have experienced and sought answers to through here. I have however pne apparent problem, when the central heating reaches the locally set temp there is a what appears to be an abrupt shut down I.e. there is a bang which can he heard through the pipework. Feels like the pump is being stopped abruptly. Any ideas if this is something which can be avoided through any setting? When I originally setup the system with CH only (no HW control) I think there was a pump overrun setting for the boiler control, but with the the HW control added there is no longer that setting.

The system comprises an evohome based controller, the hot-water pack, 12 HR92s contolling 11 different rooms, and 2 bathrooms with the original TRVs left on so they come on whenever some part of the house is being heated. To keep the wiring simple and avoid undoing what is already there, I used the terminations from the old programmer to feed the BDR91s I.e. Live and Neutral feed both BDR91's and the CH on feeds the Heating BDR91 and the HW on and HW off feed the HW BDR91. The old thermostat is then left high (i.e. always on) and the odl HW tank thermostat remains in the airing cupboard but will not reach HW temp and so is always calling for heat when asked by the Evohome. This was primarily to allow me to go back to the old system if I wanted.

Any thoughts anyone?

Were it not for the shutdown noise, I'd say it was the best system I've come across, so flexible and even the wife thinks it's a brilliant gadget.

P.S. The knowledge sharing though this forum has been an exceptional help

I think you should look at the mid position valve, when it closes it can make a noise. If it is that you'll need to check if you have a system bypass valve. What is happening is that system is all up to temperature with the radiators closed down so there is a back pressure. You may be able to get round this pressure build up by turning the pump down or leaving one radiator 'open'

But ideally get a system bypass valve installed.

[WarmBumble]

Thanks you for the feedback. I actually have two radiators (in the system) with standard TRVs on and I thought the system had a bypass value (but will expressly check) and so had not expected what you describe, but certainly worth a check as you say. I'll also look into turning the pump down and see what impact that has. Once again thanks for the ideas.

[WarmBumble]

Ok further update and it builds on what Top Brake made me think about. I looked further into the Pump and how it was being used. Its a Grundfos pump with a 3 position speed switch. BG had set it to fastest setting on installation as when the system was installed there were no TRVs fitted in the house so maximum power required. Now all bar one radiator has TRVs and number of them are permanently set low, net result is the speed and hence pressure in the system is higher than required and hence why I am getting noise. I've lowered the pump speed and so far it seems to have done the trick, but still adequate to heat the radiators which are in use.

Once again thanks for nudging my thought process in the right direction.

For DIYers such as myself another thing to consider when fitting a system such as Evohome.

[top brake]

Ok further update and it builds on what Top Brake made me think about. I looked further into the Pump and how it was being used. Its a Grundfos pump with a 3 position speed switch. BG had set it to fastest setting on installation as when the system was installed there were no TRVs fitted in the house so maximum power required. Now all bar one radiator has TRVs and number of them are permanently set low, net result is the speed and hence pressure in the system is higher than required and hence why I am getting noise. I've lowered the pump speed and so far it seems to have done the trick, but still adequate to heat the radiators which are in use.

Once again thanks for nudging my thought process in the right direction.

For DIYers such as myself another thing to consider when fitting a system such as Evohome.

Good news, glad to be of help

[top brake]

From the youlearn evohome online training:

Depending on the size and complexity of the evohome system being installed, we recommend that the installation has a Automatic Bypass circuit installed.

An Automatic Bypass Valve (DU144 or DU145) controls water flow in the Heating Circuit according to the water pressure across it and is used to maintain a minimum flow rate through the boiler and to limit circulation pressure when other water paths are closed.

A bypass circuit must be installed if the Boiler manufacturer requires one, or specifies that a minimum flow rate has to be maintained whilst the Boiler is firing.

[The EVOHOME Shop]

Long time follower - first time question
I have installed an Evohome system to replace a standard BG installed Y plan single thermostat system and having read many of the threads on this forum appear to have avoided many of the problems others have experienced and sought answers to through here. I have however pne apparent problem, when the central heating reaches the locally set temp there is a what appears to be an abrupt shut down I.e. there is a bang which can he heard through the pipework. Feels like the pump is being stopped abruptly. Any ideas if this is something which can be avoided through any setting? When I originally setup the system with CH only (no HW control) I think there was a pump overrun setting for the boiler control, but with the the HW control added there is no longer that setting.

The system comprises an evohome based controller, the hot-water pack, 12 HR92s contolling 11 different rooms, and 2 bathrooms with the original TRVs left on so they come on whenever some part of the house is being heated. To keep the wiring simple and avoid undoing what is already there, I used the terminations from the old programmer to feed the BDR91s I.e. Live and Neutral feed both BDR91's and the CH on feeds the Heating BDR91 and the HW on and HW off feed the HW BDR91. The old thermostat is then left high (i.e. always on) and the odl HW tank thermostat remains in the airing cupboard but will not reach HW temp and so is always calling for heat when asked by the Evohome. This was primarily to allow me to go back to the old system if I wanted.

Any thoughts anyone?

Were it not for the shutdown noise, I'd say it was the best system I've come across, so flexible and even the wife thinks it's a brilliant gadget.

P.S. The knowledge sharing though this forum has been an exceptional help

Sounds to me like the lack of an 'Automatic Bypass Valve' on your heating circuit and because of the lack of water flow through the radiator circuit at the end of heating demand your boiler is overheating and discharging out the heating vent pipework (hence the noise)!

On a Y Plan system the motorised zone valve will stay with the heating port open at the end of heating demand and because all TRV's are being shut down, there is no where for the water to flow hence the 'banging' as your boiler turns water into steam.

As per Top Brake suggestion, there is still a requirement for Y Plan systems to be fitted with an ABV such as the DU144 or DU145 and slowing your pump down will not stop the system overheating, you just need the correct set of factors again to cause the system to overheat. Pump speed is governed by the design of your heating system, irrespective if TRV's are fitted or not.

[WarmBumble]

I went back to check and it seems that the boiler was installed without an automatic bypass valve because at the time all bar one of the radiators had TRVs (not sure if that's typical BG process, but...). Anyhow I have made sure that the one radiator (decorative bathroom radiator) left that does not have a TRV is left fully open, to provide that function. The combination of ensuring that along with turning down the pump pressure has significant impact in terms of system water whooshing sound and also any banging. I'll investigate installation of an automated bypass valve when the boiler is next replaced, but in the mean time I'm happy with its operation. Also means I know what caused and how I can mitigate. In the mean time the Evohome works very nicely. I'm watching the thread on ideas for system improvements and will add my own once I've had a chance to live with the system more than a couple of months.

Thanks for the input/information and education.