do you mean boiler would go to lockout on overheat if all trvs shut down and the bypass valve was stuck closed? providing thr boiler had an overheat cut out/stat.
and that the rads will not get as hot as they should/did if the valve was fully open?
If you need to find a tradesperson to get your job done, please try our local search below,
or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Please select a service and enter a location to continue...
Are you a trade or supplier? You can create your listing free at DIYnot Local